Why do reactions either give out or absorb heat?
3 marks · EasyMethane reacts with oxygen as shown:
State one bond broken in the reactants.
State one bond formed in the products.
Explain, using bond breaking and making, why this reaction releases heat.
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
(a) C–H or O=O
(b) O–H in H2O
(c) More energy is released by making bonds than is required to break bonds.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States an appropriate bond broken in the reactants (e.g. C–H or O=O).
B2 (b) · 1 mark · States an appropriate bond formed in the products (e.g. O–H in H2O).
B3 (c) · 1 mark · Explains that more energy is released by making bonds than is needed to break bonds.
Worked solution
a) C–H in methane or O=O in oxygen b) O–H in H2O c) Because the energy released from bond formation in the products is greater than that required to break the bonds in the reactants.