The Student Room Group

Topic 6 Chemistry

Does a question have to specify weather temperature is being increased in the reactant or product side. Or is it just general for temperature to be increased on reactant side. Just a bit confused as that couldn't work if the endothermic reaction was the reverse reaction.
Reply 1
Original post by frlt2324
Does a question have to specify weather temperature is being increased in the reactant or product side. Or is it just general for temperature to be increased on reactant side. Just a bit confused as that couldn't work if the endothermic reaction was the reverse reaction.

The temperature of the entire reaction is increased, but the endothermic reaction benefits more from it since it requires more activation energy than what is released by the reaction, whereas the exothermic reaction already produces enough activation energy from its own reaction.
A good way to think about this is through a counter-acting change: that is, the reaction changes to reverse what ever change it is put through. So, if temperature is increased, there is more endothermic reactions (it is favoured) to reduce the amount of energy since some of it is taken in but not released. Same with pressure: if pressure increases, the reaction will make the products that overall are less dense and take up less space, so the pressure reduces. If more of a reactant is added, the reaction balances this out by making more of the product, and so on.
A few tips for these qs:

dynamic equilibrium = Where the rate of reaction for the forward and backward reactions are equal (1) / in a closed system (1)

If it is a q about explaining what will happen to the products/reactant when a change is made:

concentration/moles/mass of products/reactants will increase/decrease (1) --- because (the change) favours the forward/reverse reaction as it has less or more moles/is exothermic or endothermic/has more/less reactants (1) --- which shifts the equilibrium left (if forward) or right (if reverse) (1)

Explanation of the left/right equilibrium (cus this confused me too) is that the forward reaction happens with the left reactants and the reverse with the right reactants. If there is more of the forward reaction, more of those left reactants are used up and they take up less space, while the products are increased and they take up more space. Therefore the reaction takes place closer to the left of a chamber since there is less on the left and more on the right.

(edited 4 weeks ago)
Reply 2
Thanks a lot. So if you increase temperature it favours the endothermic side to cool it self down as it absorbs energy?. And why does decreasing temperature favour the exothermic side?
(edited 4 weeks ago)
Reply 3
Original post by frlt2324
Thanks a lot. So if you increase temperature it favours the endothermic side to cool it self down as it absorbs energy?. And why does decreasing temperature favour the exothermic side?

it means the endothermic reaction doesn't have enough energy to take in to overcome the activation energy whereas the forward reaction can sustain itself because it releases more energy than the activation energy required. Note that the rate of reaction often decreases for both, it's just that it decrease the rate of the endothermic reaction more. An example of when you need this is talking about the Haber reaction. Although the forward reaction is exothermic, in industry you use a high temperature of 450C, because the higher rate of reaction (faster reaction) produces more ammonia even though the yield per reaction decreases since the reverse reaction is favoured.
Reply 4
Thanks!

Quick Reply

Latest