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# Gas Laws

## Ideal Gas Law and the Gas Constant

### Concepts

At this point, you have experimentally explored three gas laws.

**Boyle's Law**

For a constant amount of gas at a constant temperature, the product of the pressure and volume of the gas is a constant.

*P V * = *constant*_{BL}
**Charles's Law**

For a constant amount of gas at a constant pressure, the volume of the gas is directly proportional to the absolute temperature.

*V * = *constant*_{CL} T
**Avogadro's Law**

At a given temperature and pressure, equal volumes of gas contain equal numbers of moles.

*V * = *constant*_{AL} n
In each of these laws, the identity of the gas is unimportant.

Intuitively, one expects that each of these laws is a special case of a more general law. That general law is called the Ideal Gas Law.

*P V * = * n R T*

The constant *R* is called the **gas constant**, and its physical significance will be explored in subsequent experiments.

### Experiment

**Objectives**

- Verify the applicability of the ideal gas law.
- Determine the value of the gas constant.

The molar concentration, *C*, of a gas is defined to be *C* = *n/V*. Using this definition, the ideal gas law can be rewritten as

* P * = *R T C*

In effect, the pressure of the gas should be directly proportional to both the molar concentration and the temperature.

In the previous experiment, you saw how the molar concentration of a gas can be measured experimentally. This same technique is employed in this experiment to measure the molar concentration of nitrogen at various pressures and temperatures.

To perform the experiment:

- Select a temperature
- Add nitrogen gas to the bulb
- Measure the pressure and mass of the gas
- Calculate the molar concentration of the gas
- Plot the pressure vs the molar concentration on the graph
- Repeat Steps 2-5 at least five times, so that the graph contains at least five points
- Examine the plot to determine if the ideal gas law is obeyed
- Use the slope of the plot to determine the gas constant in units of L atm mole
^{-1} K^{-1}
- Repeat the entire experiment at a different temperature. Do you obtain the same value for the gas constant?

The glass bulb has a volume of 2.00 L.

Avogadro's Law
Dalton's Law

Gas Laws Home Page

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*© 2000-2014 David N. Blauch*