Consider this system at equilibrium.
A(aq) <-> B(aq) Delta H = +750 kJ/mol ..
What can be said about Q and K immediately after an increase in temperature?
a] Q > K because Q increased..
b] Q>K because K decreased..
c] Q<K because Q decreased..
d] Q<K because K increased..
e] Q=K because neither changed
How will the system respond to the temperature increase?
a] shift to the left
b] shift to the right
c] no change
I said that it would shift to the left for the second part [i think] but for the first part i'm not sure because my notes says that adding temperature would cause the reactant concentrations to increase; thus, equilibrium constant K will decrease.
doesn't that mean that a AND b are both correct..? but there can only be one answer from part 1.. please help me reason!
A + heat ==> B
K or Q = (B)/(A)
I may not have interpreted this correctly because I'm not positive a delta T could make an IMMEDIATE impact; however, if we look at the long term, it MUST shift to the right because it's an endothermic reaction and heat is being added. So in the long term B will go up, A will go down, which means K will get larger. Therefore, in the short term Q is too small so Q < what K will be.
The reasoning is the reverse for an exothermic. reaction.
thank you Dr. Bob!
and for the sake of understanding.. can someone tell me what would happen if the reaction was exothermic instead of endothermic?
To determine the answer to the first part of the question, we need to understand the relationship between Q and K in a chemical equilibrium system.
Q represents the reaction quotient, which is calculated using the concentrations of the reactants and products at any given time during the reaction. K, on the other hand, is the equilibrium constant, which is calculated using the concentrations at equilibrium.
In this particular scenario, the reaction is endothermic since the enthalpy change is positive (+750 kJ/mol). When the temperature is increased, the system will absorb the extra heat. According to Le Chatelier's principle, when the temperature increases in an endothermic reaction, the system will respond by favoring the forward reaction to absorb the heat and try to decrease the temperature.
Now, let's consider the options:
a] Q > K because Q increased: This option is incorrect because we cannot determine the relationship between Q and K just based on the fact that Q increased.
b] Q > K because K decreased: This option is incorrect as well because increasing temperature does not necessarily lead to a decrease in K. In fact, for endothermic reactions, K may increase with temperature.
c] Q < K because Q decreased: This option is incorrect as it assumes that Q decreased, which may not be the case after a temperature increase.
d] Q < K because K increased: This option is incorrect as well because we already established that increasing temperature may not lead to an increase in K.
e] Q = K because neither changed: This option is plausible because when the reaction reaches equilibrium, Q equals K. However, immediately after a change in temperature, the reaction has not yet had time to reach equilibrium.
Therefore, option e] Q = K because neither changed is the most appropriate answer for the first part of the question. Q and K may both change, but immediately after a temperature increase, their values cannot be determined.
For the second part of the question, since the reaction is endothermic, increasing the temperature will favor the forward reaction to absorb the extra heat. Therefore, the answer is b] the system will shift to the right. The equilibrium position will shift to favor the formation of more B(aq).
Remember, equilibrium position is not the same as the equilibrium constant. The position of equilibrium refers to the relative concentrations of the reactants and products, while the equilibrium constant is a constant value that relates the concentrations of the reactants and products at equilibrium.