# Answer to Question #57262 in General Chemistry for Imran

Question #57262

How we can calculate pressure at different temp, e.g butane at 20 C & it's vapour pressure (absolute pressure) 220 kPa similarly, at 40 C is 360 kPa, at 45C is 385 kPa & 55C is 580 kPa. I want to calculate more pressure values at different temp.

Expert's answer

According to Gay-Lussac’s law the pressure of gas is proportional to the absolute temperature upon constant volume.

This can be expressed by the equation:

P=K×T, where P – the pressure, K – constant, T – the absolute temperature [T = 273 + t(in Co)].

If we need to calculate more pressure values at different temperature, the K parameter should be found:

220 kPa = K(273+20), K = 0.75085,

360 kPa = K(273+40), K = 1.1501,

385 kPa = K(273+45), K = 1.2106,

580 kPa = K(273+55), K = 1.7683

As we can see the K values are different. Calculating its average value we get an equation, which gives the pressure at given temperature:

Kav = 1.22

Answer: Thus, P = 1.22×T.

This can be expressed by the equation:

P=K×T, where P – the pressure, K – constant, T – the absolute temperature [T = 273 + t(in Co)].

If we need to calculate more pressure values at different temperature, the K parameter should be found:

220 kPa = K(273+20), K = 0.75085,

360 kPa = K(273+40), K = 1.1501,

385 kPa = K(273+45), K = 1.2106,

580 kPa = K(273+55), K = 1.7683

As we can see the K values are different. Calculating its average value we get an equation, which gives the pressure at given temperature:

Kav = 1.22

Answer: Thus, P = 1.22×T.

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## Comments

Assignment Expert16.01.16, 16:15Dear Imran.

In Pv=nRT, v, n and R are constant values. They can be neglected.

Imran11.01.16, 18:06please use for that Pv=nRT

Assignment Expert10.01.16, 16:02Using constant K. P = K × T, T = P/K, where T = 273 + t. t is a temperature in degrees Celsius, T is a temperature in degrees Kelvin.

Imran10.01.16, 15:52ok but how it is calculated 220 kPa on 20 C and vice versa all data

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