Expert's Response

What evidence in the problem statement suggests this is a Gas Law Problem?

Problem Statement:
How many mol of CH4 are in a 150 L tank exerting a pressure of 20.0 atm when the temperature is 24.0 degrees Celsius?

 

In this example there is an implicit assumption that methane, CH4 , is a gas. All of the data in the problem: pressure, temperature and volume, refer to physical properties of the gas. If there was information indicating the gas was interacting with another substance, as in a chemical reaction, we would need to use a different strategy.

 

Factoid:
The only time we see information about pressure associated with a phase other than gas is when discussing vapor pressure. Vapor pressure is associated with liquids, and is a measure of the pressure exerted by the vapor above a liquid at a given temperature. In this problem there is no mention of vapor pressure.

 

Factoid:
Normally to calculate mol of a substance we are given grams of the substance. We are not given a mass in this problem.

 

Factoid:
Any problem containing combinations of data including pressure, temperature, volume, mol, density and/or mass of a gas requires the use of the Ideal Gas Equation.

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