Chemical Formulae, Equations and Calculations Part 2
5 marks · EasyAmmonia gas is produced by the reaction of hydrogen gas with nitrogen gas at room temperature and pressure (rtp).
State the balanced chemical equation for the formation of ammonia from hydrogen and nitrogen.
What is the volume of 2 moles of hydrogen gas at rtp? Give your answer in dm³.
Convert your answer to part (b) into cm³.
If 1 mole of nitrogen gas reacts completely, how many moles of hydrogen gas are needed?
Calculate the total volume (in dm³) of all gases present after the complete reaction of 1 dm³ nitrogen gas with excess hydrogen gas at rtp. (State your assumptions about volumes in your answer.)
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) \ce{N2(g) + 3H2(g) -> 2NH3(g)} · must show Balanced chemical equation with state symbols
(b) 48 dm^3 · must show Correct multiplication: moles dm³
(c) 48,000 cm^3 · must show Correct conversion: dm³
(d) 3 mol · must show Correct use of stoichiometry
(e) 2 dm^3 (assume complete reaction; all volume appears as ammonia, with volume change due to number of moles of gas) · must show Volume of 1 dm³ N2 forms 2 dm³ NH3; state assumes ideal gas behaviour
Common mistakes: Incorrect balanced equation; Using wrong molar volume; Incorrect conversion between dm³ and cm³; Not accounting for volume change after reaction
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correct balanced equation with state symbols: \ce{N2(g) + 3H2(g) -> 2NH3(g)}
M1 (b) · 1 mark · Correct calculation for volume of 2 mol H2 using 24 dm³ per mole (2 × 24 = 48 dm³) (follow-through)
M1 (c) · 1 mark · Correct conversion of dm³ to cm³ (multiply by 1000) (follow-through)
A1 (d) · 1 mark · Correct use of stoichiometry: 3 mol H2 per 1 mol N2
B1 (e) · 1 mark · Correct calculation of volume change; states assumptions (volume relates to number of gas molecules; 2 dm³ ammonia from 1 dm³ N2 reacted, since 1 N2 produces 2 NH3; no other gases left if excess H2) (follow-through)
Worked solution
a) The balanced chemical equation is:
b) The volume of 2 moles of hydrogen at rtp is 2 × 24 dm³ = 48 dm³.
c) Convert to cm³: 48 dm³ × 1000 = 48,000 cm³.
d) From the equation, 1 mole of N2 reacts with 3 moles of H2. So 3 moles are needed.
e) 1 dm³ of N2 produces 2 dm³ of NH3. If nitrogen is completely reacted, only ammonia gas is left, so the total volume is 2 dm³ at rtp (assuming all gases measured under the same conditions and gas volumes relate to number of molecules).