Effect of Temperature on Reaction Rates

This page explores the effect of temperature on reaction rates, a crucial aspect of chemical kinetics.

When the temperature of a reaction mixture is increased, several important changes occur:

1. Reactant particles move more quickly
2. The energy of the particles increases
3. The frequency of successful collisions increases
4. The proportion of successful collisions increases

As a result of these changes, the overall rate of reaction increases with temperature.

Highlight: Increasing temperature leads to faster-moving particles with higher energy, resulting in more frequent and successful collisions, thus accelerating the reaction rate.

The page also introduces graphical representations of reaction rates:

• Fast reactions show a steeper curve
• Slow reactions display a more gradual slope

Example: A graph showing the change in total mass or volume of product over time can visually represent the difference between fast and slow reactions.

The units for rates of reaction in higher-level chemistry are introduced as mol/s.

Catalysts and Their Impact on Reaction Rates

This page focuses on investigating catalyst impact on chemical reactions and their role in altering reaction rates.

A catalyst is defined as a substance that:

1. Increases the rate of a reaction
2. Does not alter the products of the reaction
3. Is not chemically changed or used up at the end of the reaction

Definition: A catalyst is a substance that speeds up a chemical reaction without being consumed in the process.

The mechanism of catalyst action is explained:

• A catalyst provides an alternative reaction pathway
• This alternative pathway has a lower activation energy than the uncatalysed reaction

Highlight: Catalysts work by lowering the activation energy required for a reaction, thereby increasing the reaction rate without changing the overall energy change of the reaction.

The page also outlines a method to investigate the effect of changing concentration on the rate of a reaction:

1. Set up a gas syringe with a stand, boss, and clamp
2. Add 50cm³ of dilute hydrochloric acid to a conical flask
3. Add 0.4g of calcium carbonate to the flask and start a stopwatch
4. Record the volume of gas every 10 seconds
5. Clean the apparatus as directed after the reaction is complete

Example: This experimental setup can be used to measure the rate of carbon dioxide production in the reaction between calcium carbonate and hydrochloric acid.