5.1.5 Avogadro's Law

Question 1

Avogadro’s Law

Answer 1

• Avogadro’s law states that at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of gas.

Question 2

note

Answer 2

• Avogadro’s law states that at constant temperature and
  pressure, the volume of a gas is directly proportional to the number of moles of gas. As the number of moles increase, the volume increases.
• This can be stated mathematically as V n.
• Rearranging this expression yields V/n = constant.
• Since the volume divided by the number of moles is constant, the volume divided by the number of moles at an initial condition (V i /n i ) will equal the volume divided by the number of moles at a final condition (V f /n f ). This relationship can be used to solve for V i , n i , V f , or n f , given the other three variables.
• A helium balloon containing 0.10 mol of gas occupies a
  volume of 2.4 L at 25 ̊C and 1 atm. How many moles have been added if it is inflated to 5.6 L?
• The relationship V i /n i = V f /n f can be rearranged to solve for n f (the final number of moles). The number of moles added ( n) is the final number of moles (n f ) minus the initial number of moles (n i ), or 0.13 mol.

Question 3

A helium balloon with a volume of 2.4 L contains 0.10 moles of gas at 25°C and 1 atm of pressure. The balloon leaks 0.02 moles of gas until someone manages to seal the hole. What is the new volume of the balloon?

Answer 3

2 L

Question 4

Two balloons are inflated by a person blowing air into them. Balloon A contains 0.10 mol of air in a volume of 2.44 L. Balloon B contains 0.23 mol of air with a volume of 5.60 L. Assume that air contains 80% nitrogen and 20% oxygen. Is the following statement true or false? The density of air in balloon A is equal to the density of air in balloon B.

Answer 4

true

Question 5

A helium balloon at 25°C, 1 atm, has a volume of 2.88 L. Additional helium is pumped into the balloon. It now contains 1.20 g of He and its new volume is 7.20 L. How many moles of helium gas did the balloon contain originally?

Answer 5

0.12 mol

Question 6

An air bag is a safety device that protects people in a car crash by inflating a “balloon” to cushion the shock. Which of the following statements best describes how it works?

Answer 6

Gas is released by a chemical reaction of the chemicals in the air bag.

Question 7

In an experiment involving collecting gas over water at 25.0°C and 1 atm, nitrogen gas is collected in a volume of 3.16 L. The experiment continues until the volume reaches 5.75 L. What is the final number of moles of gas in the space above the water if the initial number of moles of gas is 0.20 mol?

Answer 7

0.36 mol

Question 8

Consider the following reaction at constant temperature and pressure:

CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

Which of the following statements is incorrect.

Answer 8

The total volume occupied by the reactants is equal to the volume occupied by CO2.The density of balloon A is equal to that of balloon B.

Question 9

Is the following statement true or false? At constant temperature and pressure, the volume of a gas is inversely proportional to the number of moles of gas.

Answer 9

false

Question 10

What empirical gas law is illustrated when inflating a balloon?

Answer 10

Avogadro’s law.

Question 11

In an experimental design, a sample of gas is collected over water at 25.0°C and 1 atm. The gas occupies as much volume as it “wants,” by displacing the water. The space above the water has a volume, V1, of 36.0 ml. Then more gas is bubbled through, until the new volume, V2, is 72.0 ml. The number of moles of gas in the space above the water is _______________

Answer 11

doubled

Question 12

A helium balloon contains 0.10 mol of gas and has a volume of 2.4 L (at 25°C, 1 atm). We inflate the balloon by adding 0.13 mol of helium. What is the new volume of the balloon?

Answer 12

5.5 L