L3 - energy considerations Flashcards
define enthalpy change of reaction
energy change under std. conditions
sum of energy used to break bonds and energy released when bonds are formed
define exothermic
what value of H will it be
heat lost from molecules
surroundings heat up
negative H
define endothermic
what value of H will it be
heat taken up by molecules
surroundings cool down
positive H
what value of H are reactions more likely to occur
negative
define entropy (S)
measure of dispersal of energy in a system
more disordered = higher entropy
what causes higher entropy?
higher temp
more gas molecules
when is a reaction feasible?
when G is negative
when S increases
define exergonic
negative G
define endergonic
positive G
what can happen when G = 0
can form equilibrium
can an exergonic or endergonic reaction occur spontaneously?
exergonic
how does a G = 0 reaction reach equilibrium?
the reaction in one direction (eg forward) will be more favourable so will happen more quickly at the beginning, but this will form a large amount of products which will then compensate for the slower backwards reaction
so will reach equilibrium
at equilibrium, what does a High Kc and low G°’ favour?
forward reaction
how can an energetically unfavourable reaction be achieved in the cell?
coupling with an energetically favourable one
eg ATP
