2.1 energetics

Question 0

Exothermic reactions

Answer 0

Products have less energy than the reactants, sum of reactants bonds is less

Question 1

Enthalpy change

Answer 1

Amount of heat energy transferred during a change in a system, at a constant pressure

Question 2

Endothermic reactions

Answer 2

Products have more energy than reactants, sum of reactants bonds is more than sum of products bonds

Question 3

Enthalpy of formation

Answer 3

Enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions, all reactants and products in their standard states

Question 4

Enthalpy of combustion

Answer 4

The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions, all reactants and products in their standard states

Question 5

Experiments

Answer 5

Wash, dry, initial temperature, add solid, stir, final temperature

Question 6

Errors in experiments

Answer 6

Hard to measure temperature of solids, slow reactions cool, heat loss, incomplete dissolving, assumed density and shc

Question 7

Hess’s law

Answer 7

The total enthalpy change for a reaction is independent of the route taken by the chemical change

Question 8

Working out enthalpy of formation

Answer 8

Products minus reactants

Question 9

Working out enthalpy of combustion

Answer 9

Reactants minus products

Question 10

Mean bond enthalpy

Answer 10

Enthalpy needed to break the covalent bonds in gaseous atoms, averaged over a range of compounds