Endothermic reactions

2 marks · Easy

In a laboratory experiment, a reaction gave out 120 kJ of heat when 4.0 mol of the substance were used. Calculate the enthalpy change, ΔH, for this reaction in kJ/mol. Include the correct sign in your answer.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

ΔH = –30 kJ/mol (±1)

Also accept: –30; –30 kJ/mol

Common mistakes: +30, wrong sign

Show mark scheme and worked solution

Marking points

M1 · 1 mark · Uses correct formula: ΔH = q / n, recognises that reaction gives out heat (exothermic).

A1 · 1 mark · Final answer given as –30 kJ/mol (negative sign, correct unit).

Worked solution

ΔH = q / n = –120 kJ / 4.0 mol = –30 kJ/mol