Energy changes (Mock)

Definition of exothermic?

Exothermic Reactions: Heat is transferred to surroundings (e.g combustion, neutralisation, respiration). Products have lower energy than reactants.

Definition of endothermic?

Endothermic Reactions: Energy is taken from surroundings (e.g thermal decomposition, photosynthesis). Products have higher energy than reactants.

What’s the difference between exothermic and endothermic reactions?

Exothermic reactions release energy, raising surroundings' temperature, while endothermic reactions absorb energy, lowering it.

What are energy profile diagrams?

Energy profile diagrams (or reaction profiles) are graphs showing energy changes during a reaction, with energy on the y-axis and progress on the x-axis. They illustrate activation energy as the peak, and the overall energy change between reactants and products, distinguishing between exothermic (downward) and endothermic (upward) reactions.

Graph of an exothermic reaction?

• Diagram: Products are lower than reactants.

• Profile: Energy is transferred to the surroundings, often as heat.

• Appearance: A sharp climb to the peak, followed by a larger drop to the products.

• Overall Energy Change: Negative.

Graph of an endothermic reaction?

• Diagram: Products are higher than reactants.

• Profile: Energy is absorbed from the surroundings.

• Appearance: A climb to the peak, followed by a smaller drop, leaving products higher than the starting reactants.

• Overall Energy Change: Positive.

What are the ‘Key Components of Energy Profiles’?

• Reactants & Products: The starting and ending levels.

• Activation Energy (E_a): The peak of the curve; represents the minimum energy required for a reaction to occur. It is measured from the reactant line to the top of the curve.

• Overall Energy Change (△H): The vertical distance between the reactant line and the product line.

• Reaction Path: The path from reactants over the peak (transition state) to products.

What is the key use of endothermic and exothermic reactions?

• Exothermic - Combustion, Neutralisation

• Endothermic - Thermal Decomposition, Sports Packs

Give an example of an exothermic profile?

Hand warmers

Give an example of an endothermic profile?

Cold packs