Energu Changes

What is an energy change?

Energy changes occur in all chemical reactions where energy can either be taken in or given out

Define ‘enthalpy change’

→ Enthalpy changes marks the transfer of thermal energy

What is an exothermic reaction?

→ A chemical reactions where the reactants have more thermal energy than the products.

Causing heat to be released to its surroundings.

It has a (-) enthalpy change because it is losing heat energy

What is the rule for total energy in a reaction?

Energy of reactants = energy of products

Give examples of exothermic chemical reactions

→ Oxidation

→ Combustion

→ Neutralisation

Draw a energy change diagram for exothermic reactions

→ Energy of reactants > energy of products

→ Arrow touching lines

→ Arrow of enthalpy change pointing downwards

→ activation energy arrow pointing up

What is an endothermic reaction?

→ The total energy of the product is greater than the total energy of the reactants

Meaning thermal energy must be taken in from its surroundings

The enthalpy change of the reactions is (+) because the reaction is gaining thermal energy

Give an example of an endothermic reactions

Thermal decomposition

Draw the graph for an endothermic energy change

→ Energy of reactants < Energy of products

→ Enthalpy change arrow pointing up

→ Activation energy arrow pointing up

→ Reactant line goes horizontally through

How do we calculate energy change?

Energy required to break bonds - energy required to form bonds

What value is energy change represented in ?

kJ/mol