# the temperature & the pressureThe pressure in a constant-volume gas thermometer is 0.700 atm at 100 Celsius degree and 0.512 atm at 0 Celsius degree. a) what is the temperature when the...

the temperature & the pressure

The pressure in a constant-volume gas thermometer is 0.700 atm at 100 Celsius degree and 0.512 atm at 0 Celsius degree. a) what is the temperature when the pressure is 0.040 atm? b) what is the pressure at 450 Celsius degree?

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### 2 Answers

We use the gas equation PV/T = RT to determine the temperature and pressure at the constant volume. In the formula P stands for pressure , V volume and T for temperature in kelvin which is equal to t in celsius+273.15 kelvin.Thereore,

P1V1 = R T1 gives :

0.7*0 V=R(273.15+100)..........(1) for boiling and

0.512 V= R(273.15)..................(2)

R = 1.875921211*10^(-3)V from (1) and 1.844279*10^(-3)7V from (2) for

a)

To find the temperature when P = 0.040 atm.

PV = RT . We use R value from the 2nd for lower pressure.

0.040V = (1.8442797*10^(-3)V)T. Or

T = 0.040V/[(1.8442797*10^(-3)V] = 21.3398 kelvin = (21.3398-273.15) = -251.8102 deg Celsius.

b)

To find the pressure at 450 C, we use the R from the eq(1).

PV = RT. Or

P = RT/V = [1.875921211*10^(-3)V ]* (273.15+450)/V = 1.356572 atmospheric pressure.

As the mass and volume of the gas in the thermometer is constant, the change in pressure of the gas is directly proportional to the rise of temperature. Stated in other words rise in pressure per degree rise in temperature is constant.

Given:

Pressure at 100 degrees Celsius = 0.700 atm

Pressure at 0 degrees Celsius = 0.512 atm

Therefore:

Rise in pressure for 100 degrees rise in temperature = 0.700 0.512 = 0.188 atm

Therefore:

Rise in temperature per degree Celsius rise in temperature = 0.188/100 = 0.00188 atm

Therefore:

Temperature in Celsius corresponding to any pressure p is equal to:

t = (p - p0)/(rise in pressure per degree Celsius temperature)

= (p - 0.512)/0.00188

Therefore temperature corresponding to pressure of 0.040:

= (0.040 - 0.512)/).00188 - 0.112/0.00188 = 59.57 degree Celsius.

Similarly, pressure p in atm at any given temperature t is given by:

p = p0 + t*(Rise in temperature per degree Celsius rise in temperature)

= 0.512 + t*0.00188

Therefore the pressure at 450 degree Celsius:

= 0.512 + 450*0.00188 = 0.512 + 0.846 = 1.358 atm