Rates of reactions - reaction profiles

Question 1

Enthalpy change

Answer 1

The energy change that occurs when reactants are converted to products (change in H) - can be shown in potential energy diagrams.

Question 2

Exothermic reaction

Answer 2

Products have less energy than the reactants. Heat energy has been released to the surroundings. The change in H for the reaction has a negative value to show that energy has been lost to surroundings.

Question 3

Endothermic reactions

Answer 3

Products have more energy than the reactants as energy has been taken in from the surroundings. Removing heat energy from the surroundings causes the temperature of the surroundings to fall. These reactions have a positive change in H to show energy has been gained from the surroundings.

Question 4

Activated complex

Answer 4

This is an unstable arrangement of atoms which is very high energy. In potential energy diagrams it is the very top of the activation energy diagram.

Question 5

Effect of a catalyst on energy distribution diagram.

Answer 5

Activation energy is lowered showing by decreasing the height of the curve (however it remains a curve of similar shape)