Solve Combined Gas Law: National 5 Physics Exam Help

In summary, the speaker is studying for their National 5 physics exam and is struggling with the combined gas law, P1V1/T1 = P2V2/T2. They are unsure of where they are going wrong and are seeking help from someone who can show them step-by-step how to use the formula. After receiving some advice, the speaker did some exam-style questions and now understands the formula better. They realized that their mistakes were caused by overcomplicating the equation and forgetting to convert the temperature into kelvin.
  • #1
CheesyPeeps
36
2
I am studying National 5 physics, and my exam is tomorrow. I need some last-minute help.
I'm struggling a little bit with the combined gas law, P1V1/T1 = P2V2/T2, and I'm not sure why.
It would help me a lot if you could show step-by-step how the formula is used.
Thanks for your time, it's very much appreciated.
 
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  • #2
CheesyPeeps said:
I'm struggling a little bit with the combined gas law, P1V1/T1 = P2V2/T2, and I'm not sure why.

Where exactly are you having problems with it?
 
  • #3
Drakkith said:
Where exactly are you having problems with it?

That's the problem: I'm not sure where things are going wrong. I think it may be when I substitute in the values and then have to rearrange the equation, which seems strange because usually rearranging equations is the easiest part!
 
  • #4
I'd suggest finding a homework question and posting it in the homework forums, that way the homework helpers can walk you through it and find out where you're having trouble.
 
  • #5
Okay!
Thanks a lot for your time.
 
  • #6
I'm sure I'll stop by your thread later, as we are studying the gas laws in class this week. :wink:
 
  • #7
Update: I did some exam-style questions on it and I've got it now! I think it was a mixture of me overcomplicating it and occasionally forgetting to convert the temperature into kelvin :smile:
 
  • #8
CheesyPeeps said:
and occasionally forgetting to convert the temperature into kelvin

Yes, I just clarified this with my instructor tonight. Makes sense, otherwise you end up with negative numbers when your temperature goes below zero!
 

1. What is the Combined Gas Law?

The Combined Gas Law is a gas law that combines the principles of Boyle's Law, Charles's Law, and Gay-Lussac's Law. It states that the product of pressure and volume of a gas is directly proportional to its temperature, as long as the number of moles and the gas constant remain constant.

2. How do you use the Combined Gas Law to solve problems?

To use the Combined Gas Law, you will need to know the initial pressure, volume, and temperature of the gas, as well as the final pressure, volume, and temperature. You can then substitute these values into the formula (P1V1/T1 = P2V2/T2) and solve for the missing variable. Remember to use the correct units for pressure (P), volume (V), and temperature (T).

3. What units should I use for pressure, volume, and temperature when using the Combined Gas Law?

For pressure, you should use either Pascals (Pa) or atmospheres (atm). For volume, you should use either cubic meters (m3) or liters (L). For temperature, you should use either Kelvin (K) or degrees Celsius (°C). It is important to use consistent units throughout your calculation.

4. What are some common mistakes to avoid when using the Combined Gas Law?

Some common mistakes to avoid when using the Combined Gas Law include using incorrect units, not converting temperatures to Kelvin, and not taking into account the number of moles and gas constant. It is also important to double-check your calculations and make sure they are consistent with the given conditions.

5. Can the Combined Gas Law be used for all types of gases?

No, the Combined Gas Law is only applicable for ideal gases. Real gases may deviate from the predictions of the Combined Gas Law at high pressures or low temperatures. Additionally, the Combined Gas Law should not be used for reactions involving changes in the number of moles of gas, as it assumes a constant number of moles throughout the process.

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