Amount of Substance & Gas Volume Flashcards

All 6 cards in this deck

What is the volume of one mole of any gas at room temperature and pressure (rtp)?

$24$ dm$^3$ (= $24\,000$ cm$^3$), at 20 °C and 1 atmosphere pressure.

True or false? At rtp, 1 mole of carbon dioxide occupies a larger volume than 1 mole of hydrogen because its molecules are heavier.

False. Equal amounts in moles of any gases occupy the same volume at the same temperature and pressure — both occupy $24$ dm$^3$.

What are the steps to calculate the volume of a gas at rtp from its mass?

e.g. 8 g of oxygen, $M_r(\mathrm{O_2}) = 32$

1. Moles $=$ mass $\div M_r = 8 \div 32 = 0.25$ mol
2. Volume $=$ moles $\times 24 = 0.25 \times 24$
3. $= 6$ dm$^3$

What are the steps to calculate the mass of a gas from its volume at rtp?

e.g. 48 dm$^3$ of oxygen, $M_r(\mathrm{O_2}) = 32$

1. Rearrange volume $=$ moles $\times 24$ to moles $=$ volume $\div 24 = 48 \div 24 = 2$ mol
2. Mass $=$ moles $\times M_r = 2 \times 32$
3. $= 64$ g

What are the steps to calculate the volume of a gas produced at rtp from a given mass of a solid reactant?

e.g. 10 g of $\mathrm{CaCO_3}$ in $\mathrm{CaCO_3 \rightarrow CaO + CO_2}$, $M_r(\mathrm{CaCO_3}) = 100$

1. Moles of solid $=$ mass $\div M_r = 10 \div 100 = 0.1$ mol
2. Use the equation ratio: moles $\mathrm{CO_2} = 1 : 1 = 0.1$ mol
3. Volume $= 0.1 \times 24 = 2.4$ dm$^3$

What are the steps to calculate the volume of one gas from a given volume of another gas in the same reaction?

e.g. oxygen needed for 50 cm$^3$ of hydrogen in $\mathrm{2H_2 + O_2 \rightarrow 2H_2O}$

1. Read the mole ratio from the equation: $\mathrm{H_2 : O_2} = 2 : 1$
2. Gas volumes are in the same ratio as the moles, so volume of $\mathrm{O_2} = 50 \div 2$
3. $= 25$ cm$^3$ (keep both volumes in the same unit; $1$ dm$^3 = 1000$ cm$^3$)