Question
How many mol of CH4 are in a L tank exerting a pressure of atm when the temperature is degrees Celsius?
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How many mol of CH4 are in a L tank exerting a pressure of atm when the temperature is degrees Celsius?
Problem Solving Strategy:
Since this is a problem about a gas, and all the data provided are physical properties we conclude it is an Ideal Gas Law Problem and we need to construct a table to associate values in the problem statement with the variables in the Ideal Gas Law (PV = nRT).
The Table before entering the data would look like;
V |
n |
R |
T |
Condition |
|
1 |
Completing the table with the data from the problem;
V |
n |
R |
T |
Condition |
|
atm |
? |
0.0821 L atm mol-1 K-1 |
C |
1 |
Notice there is only one condition for this gas. Before continuing we must convert all the units for each variable so they correspond to the units for R. THe units on pressure and volume agree with the units in R, but not the units on temperature. Temperature units must be Kelvins in any Ideal Gas Law Problem.
Converting degrees Celsius to Kelvins;
K = 273.15 + degrees Celsius
K = 273 + =
So the table would now look like;
V |
n |
R |
T |
Condition |
|
atm |
? |
0.0821 L atm mol-1 K-1 |
K |
1 |
Now substitute the values for each variable into the Ideal Gas Equation;
PV = nRT
Substituting;
(atm ) ( L) = n (0.0821 L atm mol-1 K-1) ( K)
Solving for the unknown, n, in the problem;
mol CH4
Summary:
1. Recognize the problem as Ideal Gas Law Problem. To help recognize the problem we note the substance is referred to as a gas either implicitly or explicitly and any information in the problem are physical properties of the substance, i.e., pressure, volume, temperature,mol, density, or mass of the gas.
2. Recognize the problem has only one condition, it is a single variable problem.
3. Write the Ideal Gas Equation; PV = nRT
4. Construct a table and assign a value from the problem statement to each of the variables in the Ideal Gas Equation.
5. Convert units of each variable intot he units corresponding to the value of R; 0.0821 L atm mol-1 K-1
6. Substitute the values into the equation and solve for the unknown.
Help Me!
How many mol of CH4 are in a L tank exerting a pressure of atm when the temperature is degrees Celsius?