Video Transcript
Under standard temperature and
pressure, STP, which of the following quantities of gas will occupy the largest
volume? (A) One mole of C2H4, (B) five
moles of H2, (C) 0.5 moles of N2, (D) two moles of Cl2, (E) three moles of O2.
Avogadro’s law states that at
constant temperature and pressure, the volume and number of moles of a gas are
directly proportional. This means that if the number of
moles of a gas are increased, the volume will also increase at the same rate. For example, one mole of gas will
occupy a certain volume. Two moles of gas will occupy twice
as much volume. The number of moles was doubled,
and the volume doubled. The amount of space a gas occupies
is dependent on the temperature and pressure. All of the gases in this question
are under standard temperature and pressure, or STP. Standard temperature and pressure
are zero degrees Celsius and one atmosphere, respectively.
At STP, one mole of any gas will
occupy a volume of 22.4 liters. Doubling the number of moles of gas
will double the volume. Thus, two moles of any gas at STP
will have a volume of 44.8 liters, and three moles of any gas at STP will have a
volume of 67.2 liters. The question asked us to determine
which quantity of gas will occupy the largest volume. As increasing the number of moles
increases the volume, we should choose the answer which has the greatest number of
moles of gas. This means that the correct answer
is answer choice (B). Five moles of hydrogen gas will
occupy the largest volume under standard temperature and pressure.
