refer to the reaction 2NH3 (g) ↔ N2 (g) + 3H2 (g), and ΔH = 92.2 kJ.
1.What will be the effect on the concentration of H2 if the temperature decreases?
A. H2 concentration will decrease.
B. H2 concentration will not change.
C. H2 concentration will increase.
D. H2 concentration will not change, but ΔH will decrease.
E. H2 concentration will not change, but pressure will increase.
2. What will be the effect on the concentration of NH3 if the pressure decreases?
A. NH3 concentration will decrease.
B. NH3 concentration will not change.
C. NH3 concentration will increase.
D. NH3 concentration will not change, but ΔH will decrease.
E. NH3 concentration will not change, but entropy will increase.
3. What will be the effect on N2 if the concentration of NH3 increases? _______
A. N2 concentration will decrease.
B. N2 concentration will not change.
C. N2 concentration will increase.
D. N2 concentration will not change, but ΔH will decrease.
E. N2 concentration will not change, but pressure will increase.
To answer these questions, you need to understand Le Chatelier's Principle, which states that when a system at equilibrium is subjected to a change, it will adjust to counteract the change and reach a new equilibrium.
1. The reaction 2NH3(g) ↔ N2(g) + 3H2(g) is an exothermic reaction (ΔH = -92.2 kJ). According to Le Chatelier's Principle, a decrease in temperature will cause the equilibrium to shift in the direction that produces heat, i.e., the reverse reaction. Therefore, the concentration of H2 will decrease.
Answer: A. H2 concentration will decrease.
2. The reaction 2NH3(g) ↔ N2(g) + 3H2(g) involves the change in pressure. Le Chatelier's Principle states that when the pressure of a system is decreased, it will shift in the direction that produces fewer gas molecules. In this case, the forward reaction produces more gas molecules (4 moles on the left, 5 moles on the right). Therefore, the equilibrium will shift to the left, resulting in a decrease in the concentration of NH3.
Answer: A. NH3 concentration will decrease.
3. When NH3 concentration increases, according to Le Chatelier's Principle, the equilibrium will shift in the direction that produces fewer NH3 molecules. In this case, it means the equilibrium will shift to the left (reverse reaction) to decrease the concentration of NH3. As a result, the concentration of N2 will decrease.
Answer: A. N2 concentration will decrease.
1. The answer is A. H2 concentration will decrease. According to Le Chatelier's principle, if the temperature decreases, the equilibrium will shift in the endothermic direction to counteract the decrease in temperature. In this case, the forward reaction is exothermic, so the equilibrium will shift to the left, resulting in a decrease in the concentration of H2.
2. The answer is A. NH3 concentration will decrease. According to Le Chatelier's principle, if the pressure decreases, the equilibrium will shift in the direction that produces more moles of gas to counteract the decrease in pressure. In this case, the forward reaction produces fewer moles of gas, so the equilibrium will shift to the left, resulting in a decrease in the concentration of NH3.
3. The answer is C. N2 concentration will increase. According to Le Chatelier's principle, if the concentration of NH3 increases, the equilibrium will shift in the direction that uses up NH3 to counteract the increase in concentration. In this case, the forward reaction uses up NH3 to produce N2, so the equilibrium will shift to the right, resulting in an increase in the concentration of N2.
This is an exercise in Le Chatelier's Principle. That principle says that a system in equilibrium will shift (that is it will move to the left or to the right) when we do something to it. The shift will be such that it will try to undo what we did to it. I'll do the backbone for you and let you do the rest of the work. Note that dH is +. That merans the reaction, just to clarify a little, i this.
2NH3 + heat ==> N2 + 3H2
So question 1 wants to know about decreasing temperature. So we ask ourselves which way will the rxn shift if we remove heat. If we take heat away the rxn will shift so as to ADD heat back. Let's look at what might happen. If the rxn shifts to the right it USES heat; if the rxn shifts to the left it ADDS heat. If we are taking it away, then the rxn will shift to the left. That means that everything on the left will get larger (the reactant side) and everything on the right (the product side) will get smaller. That is the underlying principle that will allow you to answer all of the questions. I will be glad to check your answers if you show them ALONG WITH THE REASON YOU CHOSE THAT ANSWER.