Unit 3 : Controlling the rate - REACTION PATHWAYS

Question 1

Enthlapy Change

Answer 1

The enhalpy change (delta H) is the energy difference between the products and reactants.

Enthalpy change has a negative value for exothermic reactions (downhill overall)

Enthalpy change has a positvie value for endothermic reactions (uphill overall)

Question 2

Activation energy

Answer 2

The activation energy is the minimum kinetic energy required by colliding molecules fot a reaction to occur.

Question 3

Activated complex

Answer 3

The activated complex is an unstable arrangment of atoms formed at the maximum of the potential energy barrier (top of hill), during a reaction.

Question 4

What changes happen to the potential energy diagram when a catalyst is added?

Answer 4

A catalyst provides an alternate reaction pathway with a lowering of the activation energy. Activation energy of reverse reaction is also lowered.

Enthalpy of reactants and products is unchanged. Adding a catalyst has no effect on the enthalpy change