Chemistry CCEA AS Level 2.8 (Energetics)

What is an exothermic reaction?

A reaction where the enthalpy of the products is less than the enthalpy of the reactants

What is an endothermic reaction?

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants

What is activation energy?

The energy required to break the bonds in the reactants

What are the standard pressure conditions for enthalpy changes?

1 atm

What is a standard enthalpy change?

The change in heat energy at constant pressure, measured at standard conditions

What is the standard enthalpy of a reaction?

The enthalpy change when the number of mole of substances, are as written in the equations

What is the standard enthalpy of combustion?

The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions

What is the standard enthalpy change of formation?

The enthalpy change when one mole of compound is formed from its elements under standard conditions

What is the standard enthalpy change of neutralisation?

The enthalpy change when one mole of water is produced in a neutralisation reaction under standard conditions

What is the standard enthalpy change of formation for elements?

0 kJmol-1

What is the equation to calculate enthalpy change in joules?

Q=mcΔT

What is the equation to calculate enthalpy change in kJmol-1?

ΔH = Q/n

What does Hess' law state?

The enthalpy change in a reaction is independent of the route it takes, provided the initial and final conditions are the same

What does the principle of the conservation of energy state?

Energy can neither be created nor destroyed, only changed from one form to another

What is average bond enthalpy?

The energy required to break one mole of a given bond averaged over many compounds

How is ΔH worked out using average bond enthalpy values?

ΔH = ΣBonds broken - ΣBonds made

What does the strength of a covalent bond depend on?

The atoms involved and whether the bond is single, double or triple