Why do reactions either give out or absorb heat?
2 marks · NormalState what must occur, in terms of bonds, for a reaction to be endothermic.
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
More energy must be used to break the bonds in the reactants than is released when forming bonds in the products.
Also accept: It takes more energy to break bonds than is given out making products' bonds.
Common mistakes: Confusing 'endothermic' and 'exothermic'.; Leaving out clear reference to bonds or energy.
Show mark scheme and worked solution
Marking points
B1 · 1 mark · States that more energy is needed to break bonds.
B2 · 1 mark · States that less energy is released when making new bonds.
Worked solution
For a reaction to be endothermic, more energy must be absorbed to break bonds than is released when new bonds are formed.