Hello, Arshi,
We need to assume that the volume remains constant between the two states, since it is only identified once in the question. Since the moles of gas do not change between the two states, we can use the gas law that describes the difference between two states of the same amount of gas:
P1V1/T1 = P2V2/T2
This is a result of two gas law equations (PV=nRT) for each condition that, since moles do not change, the calculation is simplified since both n, and R cancel, and we are left with the expression above.
Now it becomes an exercise in keeping the data clearly labelled (P1, P2, etc) and entering it in the equation. But remember that T in the gas laws must be in Kelvin, so add 273.15 to each C temperature.
It also helps to rearrange the equation to isolate the unknown, P2, in this case:
P2 = P1(V1/V2)(T2/T1)
Please note how I've arranged the olume and temperatures into ratios of the initial and final states. This makes it easier to visualize how the variables will impact the final volume. An added bonus is that since the volumes are the same, it quickly reduces to:
P2 = P1(V1/V2)(T2/T1)
We can see, without a calculator, that the ratio of the temperatures (in Kelvin) should reduce the pressure considerably, by (65.85/298.15), or maybe 20% from just looking at the numbers. So we should expect a redced pressurre around 1/4 of the original.
I get 38.6 kPa. The is lower by the amount we expected, so I'm content.
Bob
