# Solve Gas Law Problem: Stuck, Need Help

• apchemstudent
In summary, the conversation discussed the problem of finding the volume of water vapor at a given temperature and pressure, where the pressure changes the next day. It was mentioned that pressure and volume are not directly proportional and avogadro's law and dalton's law of partial pressures were brought up. The formula PV=nRT was also mentioned, but it was noted that it does not depend on mass composition. The conversation ended with a request for the solution to be shared with the group.
apchemstudent
I don't seem to be able to get close to any of the choices given.

Here's my work: 288 K = T
P = 101.23 kPa

2% volume = water vapor

Well the next day the pressure changes to 100.47 kPa at the same temperature. The volume changes by 101.23/100.47 = 1.008...

I'm stuck here... Can some one help? Thanks

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any idea on how to solve this problem?

apchemstudent said:
...

Well the next day the pressure changes to 100.47 kPa at the same temperature. The volume changes by 101.23/100.47 = 1.008...

...

pressure and volume are not directly proportional... perhaps this helps?

by avogadro's law the volume percent is equivalent to the mole percentage. In addition the mole percentage is equal to the pressure percentage (by dalton's law of partial pressures). Keep this in mind for the rest of this post.

I got one percent.
$$[100.47-(101.23-.02(101.23))]/100.47$$

I'm still not quite sure why they gave the molecular weight of gases in the problem, PV=nRT does not depend on mass composition. It's a colligative property

Once you find the final answer, please be considerate enough to tell the rest of us.

## What is the gas law problem?

The gas law problem is a type of physics problem that involves using the ideal gas law equation to solve for unknown variables such as pressure, volume, temperature, or number of moles.

## What is the ideal gas law equation?

The ideal gas law equation is PV = nRT, where P stands for pressure, V stands for volume, n stands for the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin.

## What are the steps to solve a gas law problem?

The first step is to identify the given variables and the unknown variable in the problem. Then, rearrange the ideal gas law equation to solve for the unknown variable. Next, plug in the given values and solve for the unknown variable using basic algebra. Finally, make sure to convert all units to the correct form (i.e. pressure in atm, volume in liters, and temperature in Kelvin).

## What are some common mistakes when solving gas law problems?

Some common mistakes include forgetting to convert units, using the wrong value for the ideal gas constant, and not considering units when rearranging the equation. It is also important to make sure that all values are in the correct units before plugging them into the equation.

## Are there any shortcuts for solving gas law problems?

One shortcut is to use the combined gas law equation, which combines the ideal gas law with Boyle's, Charles', and Gay-Lussac's laws. Another shortcut is to use a gas law calculator or app to quickly solve for the unknown variable. However, it is important to understand the steps and concepts behind solving gas law problems rather than just relying on shortcuts.

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