Question

A piece of solid carbon dioxide, with a mass of 7.8g,is placed in a 4.0-L otherwise empty container at 278C. What is the pressure in the container after all the carbon dioxide vapor- izes? If 7.8 g solid carbon dioxide were placed in the same container but it already contained air at 740 torr, what would be the partial pressure of carbon dioxide and the total pressure in the container after the carbon dioxide vaporizes?

Answer 1

Answer:

First question: P = 2.00 atm (1520 torr)

Second question: Partial pressure of carbon dioxide: 2.00 atm (1520 torr); total pressure: 2.97 atm (2260 torr).

Explanation:

The molar mass of caron dioxide, CO₂, is:

12 g/mol of C + 2*16 g/mol of O = 44 g/mol

The number of moles is the mass divided by the molar mass:

n = 7.8/44 = 0.1773 mol

By the ideal gas law:

PV = nRT

Where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant (0.082 atm*L/mol*K), and T is the temperature (278ºC + 273 = 551 K).

So, the pressure will be:

P*4 = 0.1773*0.082*551

P = 2.00 atm = 1520 torr

If there was air in the container, the partial pressure of the carbon dioxide will still the same, 2 atm (1520 torr), because the partial pressure is the pressure the substance would have if it eas alone in the container.

The total pressure is the sum of the partial pressures, so

Pt = 740 + 1520 = 2260 torr = 2.97 atm