Why do reactions either give out or absorb heat?
2 marks · EasyExplain, in terms of bond breaking and bond making, why heating calcium carbonate is endothermic.
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More energy is needed to break the bonds in calcium carbonate than is released from forming new bonds in the products.
Also accept: The energy required to break the bonds is greater than the energy released by making new bonds; More energy is absorbed in breaking bonds than is released during bond formation
Common mistakes: States only that bonds are broken without reference to energy; Says bond making absorbs energy
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Marking points
B1 · 1 mark · States that energy is needed to break bonds in calcium carbonate.
B2 · 1 mark · States that less energy is released during bond formation in the products.
Worked solution
Breaking the bonds in calcium carbonate requires more energy than is released from forming new bonds in the products. Therefore, the reaction absorbs energy (endothermic).