Chemistry Partial pressure

Question

A 1.20-g sample of dry ice (solid carbon monoxide) is added to a 755-mL flask containing nitrogen gas at a temperature of 25.0 C and a pressure of 725 mmHg. The dry ice is allowed to sublime (convert from solid to gas) and the mixture is allowed to return to 25.0 Ce. What is the total pressure in the flask?

Answer 1

The pressure before the dry ice turned into a gas was 725 mm Hg (0.954 atm). We need to find the pressure added by the dry ice. Then we can add it to the original pressure. We can do that using the ideal gas law

PV = nRT

moles of dry ice (CO₂) = 1.20 g x 1 mol CO2/44 g = 0.0273 moles (NOTE: dry ice is CO₂ not CO)

P = nRT / V = (0.0273 mol)(0.0821 Latm/Kmol)(298K) / 0.755 L = 0.885 atm

Adding this pressure to the original pressure, we have...

0.885 atm + 0.954 atm = 1.84 atm = 1398 mm Hg