Energy Change & Rates of Reactions

Question 1

heat of reaction

Answer 1

the net change of chemical potential energy of the system

Question 2

exothermic reactions

Answer 2

reactions which transform chemical potential energy into thermal energy

Question 3

endothermic reactions

Answer 3

reactions which transform thermal energy into chemical potential energy

Question 4

activation energy

Answer 4

the minimum energy required to start a chemical reaction OR the energy required to form the activated complex

Question 5

reaction rate

Answer 5

the change in concentration per unit time of either a reactant or product

Question 6

catalyst

Answer 6

substance that increases the rate of the reaction but remains unchanged at the end of the reaction

Question 7

closed system

Answer 7

one in which mass is conserved inside the system but energy can enter or leave the system freely

Question 8

open system

Answer 8

one in which both energy and matter can be exchanged between the system and its surroundings

Question 9

Le Châtelier’s principle

Answer 9

‘When an external stress (change in pressure, temperature or concentration) is applied to a system in dynamic chemical equilibrium, the equilibrium point will change in such a way as to counteract the stress’