In this question, we need to find the value of pressure of a 15 grams sample of CO2 gas, and in order to find this value, we will be using the Ideal gas law formula, which is the following:
PV = nRT
Where:
P = pressure in atm
V = volume in liters, 20 Liters
n = number of moles
R = gas constant, 0.082
T = temperature in kelvin, 0°C = 273 K
The number of moles we need to find based on the mass in the question and based on the molar mass of CO2, 44g/mol:
44g = 1 mol
15g = x moles
44x = 15
x = 15/44
x = 0.34 moles of CO2 in 15 grams
Now we have the values to add to the formula:
P * 20 = 0.34 * 0.082 * 273
20P = 7.61
P = 7.61/20
P = 0.38 atm of pressure
The pressure will be 0.38 atm