Pure Substances, Mixtures, and Catalysts

This page covers the differences between pure substances and mixtures, introduces the concept of concentration, and explains the role of catalysts in chemical reactions.

Pure substances have distinct melting and boiling points, while mixtures melt and boil over a range of temperatures.

Highlight: The sharp melting and boiling points of a substance can be used to determine its purity.

Concentration is defined as a measure of how much solute (solid) is dissolved in a solvent (liquid).

Definition: Concentration is the amount of solute dissolved in a given amount of solvent.

The page provides a detailed explanation of catalysts:

Definition: A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.

Key points about catalysts:

• They speed up reactions without being used up
• Provide an alternative reaction route with lower activation energy
• Widely used in chemical processes to increase product yield
• Enzymes are biological catalysts (large protein molecules)

Example: Enzymes in the human body act as catalysts for various biological reactions, such as the breakdown of food during digestion.

The page also introduces the concepts of exothermic and endothermic reactions:

• Exothermic reactions release energy
• Endothermic reactions absorb energy

Vocabulary: Activation energy is the minimum amount of energy required for a chemical reaction to occur.

Energy Diagrams for Exothermic and Endothermic Reactions

This page presents energy diagrams for exothermic and endothermic reactions, illustrating the energy changes that occur during these processes.

Highlight: Energy diagrams are crucial tools for understanding the energy changes in chemical reactions.

Exothermic reactions:

• Release energy to the surroundings
• The products have lower energy than the reactants
• The overall energy change is negative

Endothermic reactions:

• Absorb energy from the surroundings
• The products have higher energy than the reactants
• The overall energy change is positive

Both types of reactions require activation energy to initiate the process.

Example: The combustion of fuel is an exothermic reaction, releasing heat and light energy. In contrast, the process of photosynthesis is endothermic, absorbing energy from sunlight.

The energy diagrams clearly show the difference in energy levels between reactants and products for both types of reactions, as well as the activation energy barrier that must be overcome.

Vocabulary: The extent of reaction refers to the progress of a chemical reaction, often represented on the x-axis of energy diagrams.

These energy diagrams are essential for GCSE Chemistry and A Level Chemistry students to understand the energetics of chemical reactions and how catalysts affect the activation energy.