Consider the reaction: N2O4(g) <--> 2NO2(g)
delta H^o =58.576kJ; Keq =0.87 at 55degrees celsius
What is the effect of each of these changes upon the concentration of N2O4 at equilibrium?
a)increasing the temperature
b)increasing the volume
c) adding more NO2(g) to the system without changing pressure or temperature,
d) adding He gas to the container
e) adding a catlyst
Please help :)
This is Le Chatelier's Principle and you need to learn how to do these. They are simple but students often get confused. Most books give a very good definition but the problem is that most students don't follow it. My unorthodox definition is this. When a system in equilibrium is subjected to a stress the system will try to undo what we've done to it. That means if we add a reagent or heat it will shift so as to undo what we did.
Note that the reaction is endothermic; ie., we can write heat on the LEFT side. So if we increase T it will try to undo that. How can it do that? It can react more of the reactants to form more products. That's how it can use up the added heat. If we add N2O4 it will shift to the right in order to use up the added N2O4. With increasing pressure the system will shift to the side with the fewer moles of gas.
Post your answers if you want someone to check them.
Thank you! :)
a) Increasing the temperature: According to Le Chatelier's principle, increasing the temperature will shift the reaction in the endothermic direction to absorb the excess heat. In this case, increasing the temperature will favor the formation of NO2(g), resulting in a decrease in the concentration of N2O4 at equilibrium.
b) Increasing the volume: Increasing the volume will decrease the pressure. According to Le Chatelier's principle, the system will try to counteract this change by favoring the side with more moles of gas. In this case, the reaction shows a decrease in moles of gas (N2O4 is a gas and 2NO2 has more moles of gas), so increasing the volume will favor the formation of more moles of gas. As a result, the concentration of N2O4 at equilibrium will decrease.
c) Adding more NO2(g) to the system without changing pressure or temperature: Adding more NO2(g) will increase its concentration in the system. According to Le Chatelier's principle, the system will react to counteract this change. In this case, the reaction will shift towards the left (reverse reaction) to use up the excess NO2(g). As a result, the concentration of N2O4 at equilibrium will increase.
d) Adding He gas to the container: Adding an inert gas, such as He gas, will not have a significant effect on the reaction. It will only increase the total pressure of the system, but not change the concentrations of N2O4 or NO2. Therefore, the concentration of N2O4 at equilibrium will remain the same.
e) Adding a catalyst: A catalyst increases the rate of a reaction without being consumed in the process. It does not affect the position of equilibrium or the concentrations of reactants and products at equilibrium. Therefore, adding a catalyst will not have any effect on the concentration of N2O4 at equilibrium.
To determine the effect of each change on the concentration of N2O4 at equilibrium, you need to analyze Le Chatelier's principle. According to this principle, if a system at equilibrium experiences a change in conditions, the system will shift in a way that minimizes the impact of the change.
a) Increasing the temperature:
According to Le Chatelier's principle, increasing the temperature will favor the endothermic reaction to absorb the added heat. In this case, the forward reaction (N2O4(g) → 2NO2(g)) is endothermic because it absorbs heat. Therefore, increasing the temperature will shift the equilibrium to favor the reactants. As a result, the concentration of N2O4 will decrease at equilibrium.
b) Increasing the volume:
If the volume is increased, the equilibrium will shift in the direction that reduces the number of gas molecules. In this case, the reaction shows a decrease in the number of molecules from reactants to products. Thus, increasing the volume will favor the side with fewer gas molecules. As a result, the concentration of N2O4 at equilibrium will decrease.
c) Adding more NO2(g) to the system without changing pressure or temperature:
Since no change is made to the temperature or pressure, adding more NO2(g) will increase the concentration of one of the products. According to Le Chatelier's principle, the system will shift towards the side with fewer moles of gas to reduce the excess. Therefore, the equilibrium will shift to favor the reverse reaction, resulting in an increase in the concentration of N2O4.
d) Adding He gas to the container:
He gas is inert and does not participate in the reaction. Adding an inert gas will increase the total pressure in the system without affecting the partial pressures of the reactants or products. No shift in the equilibrium position will occur, so the concentration of N2O4 will remain unaffected.
e) Adding a catalyst:
A catalyst increases the rate of a chemical reaction without being consumed in the process. It does not shift the position of the equilibrium. Therefore, adding a catalyst will not change the concentration of N2O4 at equilibrium.
In summary:
a) Increasing temperature: Concentration of N2O4 decreases.
b) Increasing volume: Concentration of N2O4 decreases.
c) Adding more NO2(g): Concentration of N2O4 increases.
d) Adding He gas: Concentration of N2O4 remains unaffected.
e) Adding a catalyst: Concentration of N2O4 remains unaffected.