Gce Model Questions Vol1 2017 Chemistry Question 40

Practice objective / multiple choice question 40 from the 2017 Gce Model Questions Vol1 Chemistry examination.

Gce Model Questions Vol1 2017 Chemistry Objective / Multiple Choice Hard Difficulty
Question 40 GCE_MODEL_QUESTIONS_VOL1 • 2017 • CHEMISTRY • objective

The standard enthalpies of formation are \(\Delta_f H^{\circ}(CO_{2}) = -393.5\ \text{kJ\,mol}^{-1}\) and \(\Delta_f H^{\circ}(SiO_{2},\text{quartz}) = -910.9\ \text{kJ\,mol}^{-1}\). When carbon and silicon combust completely in oxygen they form CO₂ and SiO₂ respectively: \(C + O_{2} \rightarrow CO_{2}\) and \(Si + O_{2} \rightarrow SiO_{2}\).\n\n(a) Calculate the energy released per gram of carbon and per gram of silicon.\n(b) Calculate the energy released per mole of O₂ consumed for each reaction.\n(c) Based on these results, which element releases more energy per gram, and which releases more per mole of O₂? Explain the apparent discrepancy.

Answer Options

A. Energy per gram: C = 33.5 kJ g⁻¹, Si = 31.8 kJ g⁻¹; Energy per mole O₂: C = 400.0 kJ mol⁻¹, Si = 900.0 kJ mol⁻¹. Thus per gram Si releases more, per mole O₂ C releases more.
B. Energy per gram: C = 30.0 kJ g⁻¹, Si = 35.0 kJ g⁻¹; Energy per mole O₂: C = 350.0 kJ mol⁻¹, Si = 950.0 kJ mol⁻¹. Thus per gram Si releases more, per mole O₂ Si releases more.
C. Energy per gram: C = 32.8 kJ g⁻¹, Si = 32.4 kJ g⁻¹; Energy per mole O₂: C = 393.5 kJ mol⁻¹, Si = 910.9 kJ mol⁻¹. Thus per gram both elements release the same energy, and per mole O₂ both release the same energy.
Correct Answer D. Energy per gram: C = 32.8 kJ g⁻¹, Si = 32.4 kJ g⁻¹; Energy per mole O₂: C = 393.5 kJ mol⁻¹, Si = 910.9 kJ mol⁻¹. Thus per gram C releases more, per mole O₂ Si releases more (difference due to different molar masses).
Correct Answer
D
Correct Option:
Energy per gram: C = 32.8 kJ g⁻¹, Si = 32.4 kJ g⁻¹; Energy per mole O₂: C = 393.5 kJ mol⁻¹, Si = 910.9 kJ mol⁻¹. Thus per gram C releases more, per mole O₂ Si releases more (difference due to different molar masses).

About This Question

This is Gce Model Questions Vol1 2017 Chemistry Question 40. It is one of the objective questions from the 2017 Gce Model Questions Vol1 Chemistry examination.

Difficulty level: Hard .

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