Choice of pressure when using ideal gas equation

In summary, the conversation discussed the use of a weighted piston-cylinder device containing 100g of CO. The CO was initially at 1000kPa and 200°C and then heated until 500°C. The final volume of the CO was determined using the ideal gas law, with the original pressure of 1000kPa being used instead of the final pressure. This is because the initial and final pressure are considered equal as long as the weight remains the same. Alternatively, Charles Law could also be used to calculate the final volume, using the initial volume calculated from the ideal gas law.
  • #1
jasoncurious
8
0
100g of CO are contained in a weighted piston-cylinder device. Initially, the CO is at 1000kPa and 200°C. It is then heated until 500°C. Determine the final volume of the CO treating it as an ideal gas.

This is what my lecturer gave in his solution:

V2=(mRT2)/P=(0.1kg*0.2968kPa.m3/kg.K*(500+273)K)/1000kPA

My question is: why is the original pressure (1000kPa) been used instead of the final pressure?

Thanks for your help.
 
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  • #2
Because initial and final pressure are equal as long as the weight on the cylinder remains the same.
 
  • #3
You can also use Charles Law to calculate the final volume, having calculated the initial volume from the universal gas law.
 

1. What is the ideal gas equation?

The ideal gas equation, also known as the ideal gas law, is a mathematical relationship between pressure (P), volume (V), temperature (T), and the number of moles (n) of a gas. It is expressed as PV = nRT, where R is the universal gas constant.

2. How do I choose the pressure to use in the ideal gas equation?

The pressure used in the ideal gas equation should be in the same units as the other variables. It is important to use the correct units in order to get an accurate result. Common units for pressure include atmospheres (atm), pascals (Pa), and millimeters of mercury (mmHg).

3. Can the pressure in the ideal gas equation be negative?

No, the pressure in the ideal gas equation cannot be negative. This is because pressure is a measure of the force exerted by gas molecules on the walls of its container. A negative pressure would indicate that the gas is pushing inward instead of outward.

4. How does the choice of pressure affect the ideal gas equation?

The pressure in the ideal gas equation affects the volume and temperature of the gas. As pressure increases, volume decreases and temperature increases, and vice versa. This relationship is known as Boyle's Law and Charles's Law, respectively.

5. Is the ideal gas equation only applicable to ideal gases?

No, the ideal gas equation can also be used for real gases under certain conditions, such as low pressure and high temperature. However, it is not always accurate for real gases and more complex equations, such as the van der Waals equation, may be needed in these cases.

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