AP Chemistry Question of the Day --16

Welcome back to my blog. I just got back from a camping trip. It was fun enjoying the last bit of summer before school starts. 

Here comes the answer to question 15 I posted yesterday. The correct answer is B. 

From the reaction equation, we can see that one molecule of PCl5 will produce 1 molecule of PCl3 and 1 molecules of Cl2.

If the reaction goes to completion, the mole number of the product is double that of the reactants. According to ideal gas law: PV=nRT, when the temperature and the volume are held constant, the total pressure is directly proportional to the total mole number. Since at the beginning the pressure was 1atm and in the end the mole number doubled. As a result, the pressure doubled too.

So, B is the right answer.

Following is Question 16 of the series. It is in continuation with question 12, 13, 14 and 15. 

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. Additional Cl2(g) is injected into the system at equilibrium. Which of the following graphs best shows the rate of the reverse reaction as a function of time? (Assume that the time for injection and mixing of the additional Cl2(g) is negligible.)

I will post the answer and explanation tomorrow. 

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