Energetics

Question 1

Define the standard molar enthalpy of combustion

Answer 1

The energy change when one mole of a substance is burnt completely in oxygen with all reactants and products in standard states at 100kPa and a stated temperature

Question 2

Define activation energy

Answer 2

The minimum energy required by particles for a reaction to occur

Question 3

State Hess’ law

Answer 3

The enthalpy change in a reaction is independent of the route taken and depends only on the initial and final states

Question 4

Define the standard molar enthalpy of formation

Answer 4

The enthalpy change when 1 mole of a substance is formed from its constituent elements in their standard states at 100kPa and a stated temperature

Question 5

Describe a Hess cycle using enthalpies of combustion

Answer 5

Arrows from original equation down to products of combustion
Σenthapies of combustion of reactants - Σenthalpies of combustion of products

Question 6

Describe a Hess cycle using enthalpies of formation

Answer 6

Arrows from elements up to original equation
Σenthapies of formation of products - Σenthalpies of formation of reactants

Question 7

Define enthalpy

Answer 7

Heat energy change at constant pressure