Endothermic reactions
2 marks · NormalA reaction absorbs 150 kJ of heat energy when exactly 3.0 mol of the reactant react completely.
Calculate the enthalpy change, ΔH, for this reaction in kJ/mol.
Show your working. Include the correct sign.
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.
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ΔH = +50 kJ/mol (±0.5)
Also accept: +50 kJ/mol; 50 kJ/mol (with explanation)
Common mistakes: -50 kJ/mol (wrong sign); dividing moles by energy
Show mark scheme and worked solution
Marking points
M1 · 1 mark · Uses correct method: divides total heat energy by moles ()
A1 · 1 mark · Correct value (+50 kJ/mol) with positive sign for endothermic reaction
Worked solution
The enthalpy change per mole (ΔH) is calculated by dividing the total heat absorbed by number of moles:
ΔH is positive as the reaction is endothermic.