Thermochemistry

What is heat of reaction

Heat change that occurs when a reaction takes place according to a given balanced chemical equation.

What is an exothermic reaction

A reaction that gives out heat to the surroundings

What is the sign of ΔH for an exothermic reaction

Negative

What is an endothermic reaction

A reaction that takes in heat from the surroundings

What is the sign of ΔH for an endothermic reaction

Positive

What is heat of combustion

Heat change when 1 mole of a substance burns in excess oxygen

What are the units of heat of combustion

kJ mol⁻¹

What apparatus measures heat of combustion accurately

Bomb calorimeter

What is kilogram calorific value

Heat produced when 1 kg of fuel burns in excess oxygen

What are the units of kilogram calorific value

kJ kg⁻¹

Why compare kilogram calorific values

To compare fuel efficiency

What is heat of formation

Heat change when 1 mole of a substance forms from its elements in standard states

What are the units of heat of formation

kJ mol⁻¹

Why are heats of formation harder to measure

Other products may form along with main product

What does Hesss law say

if a chemical reaction takes place in several stages, then the sum of the individual stages equals the heat change as if the reaction had been carried out in one single stage.

What is bond energy

Energy required to break 1 mole of covalent bonds and separate neutral atoms completely