Nonrenewable Energy & Fossil Fuels — Practice · Grade 12 Science

Chapter: Energy, Water & Material Resources

What this practice covers

By the end of Nonrenewable Energy & Fossil Fuels you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: fossil fuel, combustion, hydraulic fracturing (fracking), nuclear fission.

Problem 1

Which of the following is a fossil fuel?
  1. Wind
  2. Coal
  3. Uranium
  4. Sunlight
Answer and explanation

Coal

Coal, oil, and natural gas are the three fossil fuels. Uranium is a nuclear fuel, and sunlight and wind are renewable.

Problem 2

Which fossil fuel typically releases the LEAST carbon dioxide per unit of energy when burned?
  1. Coal
  2. Oil (petroleum)
  3. Natural gas
  4. Peat
Answer and explanation

Natural gas

Natural gas emits roughly half the CO2 of coal per kilowatt-hour, which is why it is often called a 'cleaner' fossil fuel.

Problem 3

Coal emits about 2.2 lb of CO2 per kWh and natural gas about 0.9 lb per kWh. How many pounds of CO2 are avoided by generating 1,000 kWh with natural gas instead of coal?
Answer and explanation

1300 lb

Coal: 2.2 x 1,000 = 2,200 lb. Gas: 0.9 x 1,000 = 900 lb. Avoided: 2,200 - 900 = 1,300 lb.

Problem 4

Nuclear power plants generate energy mainly through which process?
  1. Nuclear fusion of hydrogen nuclei
  2. Ordinary radioactive decay of coal
  3. Combustion of uranium in air
  4. Nuclear fission — splitting heavy nuclei like uranium-235
Answer and explanation

Nuclear fission — splitting heavy nuclei like uranium-235

A nuclear plant splits heavy uranium-235 nuclei (fission), releasing heat that boils water to spin a turbine — no burning is involved.

Problem 5

Which statement about nuclear power is TRUE?
  1. It emits almost no CO2 while operating but produces long-lived radioactive waste
  2. It is a renewable energy source like solar
  3. It releases more CO2 per kWh than coal
  4. It cannot provide steady, around-the-clock electricity
Answer and explanation

It emits almost no CO2 while operating but produces long-lived radioactive waste

Nuclear power is nearly carbon-free during operation and runs reliably as baseload power, but it produces radioactive waste that stays hazardous for thousands of years, and uranium is nonrenewable.

Problem 6

Natural gas is often called a 'cleaner' fossil fuel than coal, yet scientists warn that its climate benefit can be undercut. Explain why, using the term methane.
Answer and explanation

Burning natural gas releases only about half the CO2 of coal per unit of energy, which is the source of its 'cleaner' reputation. But natural gas is mostly methane, a powerful greenhouse gas, and some of it leaks unburned into the atmosphere during drilling, storage, and transport. Because methane traps far more heat than CO2 (especially in the short term), those leaks can cancel out much of the CO2 advantage.

Problem 7

A plant converts 200 MJ fuel to 80 MJ electricity. Find efficiency. Show the reasoning, not just the conclusion.
Hints

Compare energy at the same system boundary.

Answer and explanation

40%.

Problem 8

Why is a fuel considered nonrenewable on human timescales?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Its formation/replenishment is much slower than extraction and use.

Problem 9

Trace upstream and downstream effects instead of using one labelTrace upstream and downstream effects instead of using one labelExtractionLeaks / land / waterProcessing /transportEnergy / lossesCombustion /serviceCO₂ / pollutantsLife-cycle boundary includes more than the smokestack.Different pollutants require their own quantities and impact models.
Original pathway inventory; no current plant emission factor or universal fuel ranking is asserted.
Interpret the supplied visual. Why can a lower combustion CO₂ factor be insufficient for a full climate ranking?
Answer and explanation

Upstream methane, conversion efficiency and other life-cycle emissions can change the result under the stated horizon/boundary.

A fuel life cycle includes extraction, processing, transport, conversion and residual management. Direct CO₂, methane leakage, particulates, sulfur compounds and land/water effects are different pathways that need separate evidence. “Cleaner” is incomplete without naming the pollutant, service and boundary. A climate comparison using CO₂-equivalent values also needs a stated time horizon and conversion method; it is not simply a count of molecules emitted.

Upstream methane, conversion efficiency and other life-cycle emissions can change the result under the stated horizon/boundary.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 10

Plant A delivers 40 MJ electricity from 100 MJ fuel; B delivers 50 MJ from 100 MJ. Direct fuel factors are 80 and 70 g CO₂/MJ input. Compare direct emissions per delivered MJ, then name an omitted term.
Answer and explanation

A:8000/40=200 g/MJ delivered. B:7000/50=140 g/MJ. Upstream leakage, transport or construction is omitted; this direct comparison is not a complete life-cycle ranking.

A:8000/40=200 g/MJ delivered.

B:7000/50=140 g/MJ.

Upstream leakage, transport or construction is omitted; this direct comparison is not a complete life-cycle ranking.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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