STUDENT SPACE · TOPIC 3

Gas volumes at room conditions

Use molar gas volume and gas ratios, including a purity calculation.

The essentials

Key vocabulary

EnglishChinese
molar gas volume气体摩尔体积
room temperature and pressure室温和常压
volume ratio体积比

Quick practice

Try each question before opening its hint or answer. Use paper for calculations and diagrams.

Question 1

A student calculates 480 ÷ 24 = 20 mol for 480 cm³ gas at RTP. Correct the calculation.

Need a hint for Question 1?

Use the relationships above and check particle ratios and units.

Check Question 1

480/24 000 = 0.0200 mol, or 0.480/24 = 0.0200 mol.

Question 2

CaCO₃ → CaO + CO₂. Find the CO₂ volume at RTP from complete decomposition of 2.50 g pure CaCO₃. M(CaCO₃) = 100 g/mol; molar gas volume = 24 dm³/mol.

Need a hint for Question 2?

Convert carbonate mass to moles, use the ratio, then multiply by 24.

Check Question 2

n = 2.50/100 = 0.0250 mol; V = 0.600 dm³ = 600 cm³.

Question 3

N₂(g) + 3H₂(g) → 2NH₃(g). What volume of H₂ reacts with 20 cm³ N₂ at the same temperature and pressure?

Need a hint for Question 3?

At the same temperature and pressure, gaseous volumes follow the mole ratio.

Check Question 3

H₂ volume = 3 × 20 = 60 cm³.

Use Lesson 3 in your worksheet for written practice. Your teacher will discuss those answers in class.

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