AP Chemistry Question of the Day --13

Here comes the answer to question 12 I posted yesterday. The correct answer is C. 

According to ideal gas law,

PV=nRT

Since the temperature and volume are held constant, pressure (P) is directly proportional to total mole number. As one molecule of PCl5 will produce 2 molecules of product.  At equilibrium, there are more moles of gas in the container, causing the pressure to increase. So, C is the right answer.

Following is Question 13 of the series. It is in continuation with question 12. 

13. PCl5(g) decomposes into PCl3(g) and Cl2(g) according to the equation above. A pure sample of PCl5(g) is placed in a rigid, evacuated 1.00 L container. The initial pressure of the PCl5(g) is 1.00 atm. The temperature is held constant until the PCl5(g) reaches equilibrium with its decomposition products. The figures below show the initial and equilibrium conditions of the system. As the reaction progresses toward equilibrium, the rate of the forward reaction

(A) increases until it becomes the same as the reverse reaction rate at equilibrium
(B) stays constant before and after equilibrium is reached
(C) decreases to become a constant nonzero rate at equilibrium
(D) decreases to become zero at equilibrium

I will post the answer and explanation tomorrow.

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