Subjects
Biology
Chemistry
AP Chemistry
English
AP English Literature
Chemistry
Dec 5, 2025
81
6 pages
Measuring enthalpy changes might sound complicated, but it's actually just about calculating how much heat energy gets absorbed... Show more
The foundation of measuring enthalpy changes is the heat energy equation q = mcΔT. This formula calculates the heat energy in Joules that's transferred into or out of a material during a reaction.
Here's what each letter represents q is the heat energy in Joules, m is the mass of the material in grams, c is the specific heat capacity, and ΔT is the temperature change in Kelvin. For water, which you'll use in most experiments, the specific heat capacity is always 4.18 J g⁻¹K⁻¹.
Quick Tip Remember that temperature change in Celsius equals temperature change in Kelvin, so you don't need to convert your temperature readings!
Once you've calculated q in Joules, you need to convert it to the standard kJ mol⁻¹ format that appears in exams. This involves a simple four-step process that becomes second nature with practice.
First, convert Joules to kilojoules by dividing by 1000. Then calculate the number of moles of the substance in your system - this could be fuel, limiting reagent, water, or product formed depending on your experiment.
Next, scale up from your calculated moles to 1 mole using the formula ΔH = q (in kJ) × . Finally, add the correct sign positive for endothermic reactions (absorbing heat) and negative for exothermic reactions (releasing heat).
Exam Focus Most reactions you'll encounter are exothermic, so expect negative ΔH values in your answers!
Combustion experiments use a spirit burner and conductive calorimeter to measure enthalpy of combustion. In this methanol example, 150 cm³ of water was heated from 21.5°C to 62.5°C whilst burning methanol.
The calculation follows our standard steps q = 150 × 4.18 × (62.5 - 21.5) = 25,707 J = 25.707 kJ. The mass of methanol burned was 1.60g (196.97 - 195.37), giving 0.05 moles when divided by methanol's molar mass of 32.
Scaling up to 1 mole ΔcH = 25.707 × (1/0.05) = -514 kJ mol⁻¹. The negative sign indicates this combustion reaction releases energy, which makes sense for burning fuel.
Practical Tip Always weigh the spirit burner before and after to find the exact mass of fuel burned!
Displacement reactions like zinc replacing copper use insulated calorimeters to measure enthalpy changes. Here, 50 cm³ of 1.00 mol/dm³ CuSO₄ solution reacted with zinc, heating the solution from 22.5°C to 60.5°C.
The heat calculation gives q = 50 × 4.18 × (60.5 - 22.5) = 7,942 J = 7.942 kJ. The moles of limiting reagent (CuSO₄) = 0.05 mol from the volume and concentration given.
Scaling to standard conditions ΔrH = 7.942 × (1/0.05) = -159 kJ mol⁻¹. This negative value shows the displacement reaction releases energy when zinc displaces copper from solution.
Remember Use the limiting reagent's moles for scaling - this is usually determined by the reaction equation!
When two solutions mix in precipitation or neutralisation reactions, you add their volumes together for the mass calculation. This example shows a silver nitrate precipitation where the total volume becomes 25 cm³.
The temperature rose from 19.5°C to 47.5°C, giving ΔT = 28°C. Using our formula q = 25 × 4.18 × 28 = 2,926 J = 2.926 kJ. The moles of AgNO₃ = 0.025 × 0.512 = 0.0128 mol.
The scaling calculation becomes ΔrH = 2.926 × (2/0.0128) = -457 kJ mol⁻¹. Notice the factor of 2 in the scaling - this comes from the balanced equation showing the stoichiometric ratio.
Key Point Always check the balanced equation to get the correct mole ratio for scaling!
Cooling curves help you get more accurate ΔH values by accounting for heat loss to surroundings. You plot temperature against time and extrapolate back to find what the maximum temperature would have been without heat loss.
The graph shows temperature rising sharply when reactants mix, then gradually falling as heat escapes. By drawing a line back from the cooling section, you can estimate the true maximum temperature that would occur in a perfectly insulated system.
This technique is particularly important for slower reactions where significant cooling occurs before you can measure the peak temperature. Using the corrected temperature gives you a more accurate enthalpy value.
Exam Technique You might need to read maximum temperature values from cooling curve graphs, so practise interpreting these diagrams!
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Hess's Law
ChemistryExplore the Haber Process for ammonia synthesis, including reaction conditions, catalyst use, and the production of NPK fertilisers. Understand the impact of temperature and pressure on yield, and the environmental implications of fertiliser use. This summary provides essential insights for chemistry students.
ChemistryExplore the principles of Gibbs Free Energy, including enthalpy and entropy changes, thermodynamic favorability, and spontaneity. This summary covers key concepts such as standard entropy and enthalpy changes, providing essential insights for understanding chemical reactions and their feasibility. Ideal for students studying thermodynamics.
Chemistrytemperature vs heat, endothermic & exothermic, thermodynamic calculations (phase change including heat of fusion, vaporization; temperature change using q=mc/\T; enthalpy of reaction), entropy & gibbs free energy
AP ChemistryNotes relating to phase change: triple point, critical points, and heating curves.
AP ChemistryNotes on the topic
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Measuring enthalpy changes might sound complicated, but it's actually just about calculating how much heat energy gets absorbed or released during chemical reactions. You'll use a straightforward formula and follow clear steps to work out these values, which are essential... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The foundation of measuring enthalpy changes is the heat energy equation: q = mcΔT. This formula calculates the heat energy in Joules that's transferred into or out of a material during a reaction.
Here's what each letter represents: q is the heat energy in Joules, m is the mass of the material in grams, c is the specific heat capacity, and ΔT is the temperature change in Kelvin. For water, which you'll use in most experiments, the specific heat capacity is always 4.18 J g⁻¹K⁻¹.
Quick Tip: Remember that temperature change in Celsius equals temperature change in Kelvin, so you don't need to convert your temperature readings!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Once you've calculated q in Joules, you need to convert it to the standard kJ mol⁻¹ format that appears in exams. This involves a simple four-step process that becomes second nature with practice.
First, convert Joules to kilojoules by dividing by 1000. Then calculate the number of moles of the substance in your system - this could be fuel, limiting reagent, water, or product formed depending on your experiment.
Next, scale up from your calculated moles to 1 mole using the formula: ΔH = q (in kJ) × . Finally, add the correct sign: positive for endothermic reactions (absorbing heat) and negative for exothermic reactions (releasing heat).
Exam Focus: Most reactions you'll encounter are exothermic, so expect negative ΔH values in your answers!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Combustion experiments use a spirit burner and conductive calorimeter to measure enthalpy of combustion. In this methanol example, 150 cm³ of water was heated from 21.5°C to 62.5°C whilst burning methanol.
The calculation follows our standard steps: q = 150 × 4.18 × (62.5 - 21.5) = 25,707 J = 25.707 kJ. The mass of methanol burned was 1.60g (196.97 - 195.37), giving 0.05 moles when divided by methanol's molar mass of 32.
Scaling up to 1 mole: ΔcH = 25.707 × (1/0.05) = -514 kJ mol⁻¹. The negative sign indicates this combustion reaction releases energy, which makes sense for burning fuel.
Practical Tip: Always weigh the spirit burner before and after to find the exact mass of fuel burned!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Displacement reactions like zinc replacing copper use insulated calorimeters to measure enthalpy changes. Here, 50 cm³ of 1.00 mol/dm³ CuSO₄ solution reacted with zinc, heating the solution from 22.5°C to 60.5°C.
The heat calculation gives: q = 50 × 4.18 × (60.5 - 22.5) = 7,942 J = 7.942 kJ. The moles of limiting reagent (CuSO₄) = 0.05 mol from the volume and concentration given.
Scaling to standard conditions: ΔrH = 7.942 × (1/0.05) = -159 kJ mol⁻¹. This negative value shows the displacement reaction releases energy when zinc displaces copper from solution.
Remember: Use the limiting reagent's moles for scaling - this is usually determined by the reaction equation!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
When two solutions mix in precipitation or neutralisation reactions, you add their volumes together for the mass calculation. This example shows a silver nitrate precipitation where the total volume becomes 25 cm³.
The temperature rose from 19.5°C to 47.5°C, giving ΔT = 28°C. Using our formula: q = 25 × 4.18 × 28 = 2,926 J = 2.926 kJ. The moles of AgNO₃ = 0.025 × 0.512 = 0.0128 mol.
The scaling calculation becomes: ΔrH = 2.926 × (2/0.0128) = -457 kJ mol⁻¹. Notice the factor of 2 in the scaling - this comes from the balanced equation showing the stoichiometric ratio.
Key Point: Always check the balanced equation to get the correct mole ratio for scaling!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Cooling curves help you get more accurate ΔH values by accounting for heat loss to surroundings. You plot temperature against time and extrapolate back to find what the maximum temperature would have been without heat loss.
The graph shows temperature rising sharply when reactants mix, then gradually falling as heat escapes. By drawing a line back from the cooling section, you can estimate the true maximum temperature that would occur in a perfectly insulated system.
This technique is particularly important for slower reactions where significant cooling occurs before you can measure the peak temperature. Using the corrected temperature gives you a more accurate enthalpy value.
Exam Technique: You might need to read maximum temperature values from cooling curve graphs, so practise interpreting these diagrams!
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
2
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Hess's Law
ChemistryExplore the Haber Process for ammonia synthesis, including reaction conditions, catalyst use, and the production of NPK fertilisers. Understand the impact of temperature and pressure on yield, and the environmental implications of fertiliser use. This summary provides essential insights for chemistry students.
ChemistryExplore the principles of Gibbs Free Energy, including enthalpy and entropy changes, thermodynamic favorability, and spontaneity. This summary covers key concepts such as standard entropy and enthalpy changes, providing essential insights for understanding chemical reactions and their feasibility. Ideal for students studying thermodynamics.
Chemistrytemperature vs heat, endothermic & exothermic, thermodynamic calculations (phase change including heat of fusion, vaporization; temperature change using q=mc/\T; enthalpy of reaction), entropy & gibbs free energy
AP ChemistryNotes relating to phase change: triple point, critical points, and heating curves.
AP ChemistryNotes on the topic
ChemistryApp Store
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Sociology
Biology