How much time should I spend on each Unit 6 FRQ?

The free-response section gives 70 minutes for three FRQs, so budget roughly 22 minutes each and leave a few minutes to review calculations and units. If one part stumps you, move on — parts are scored independently.

Do I lose points for wrong arithmetic if my setup is correct?

Usually not all of them. Calculation points are often split between correct setup with units and the correct final value. If your equation, substitution, and units are right but you make a small math error, you typically still earn most of the credit, which is why showing every step matters.

What is the most common reason students lose easy FRQ points on energy questions?

Two things: dropping units in calculations so graders cannot verify the answer, and giving vague proposals like "use renewables" without naming a specific technology and explaining the mechanism that reduces the problem. Specificity and units recover those points.

Do I need to memorize energy formulas for the FRQ section?

Yes. Know E = P × t, the efficiency formula, and metric prefix conversions (kilo, mega, giga differ by factors of 1000). The exam expects you to set up and complete calculations without a provided equation sheet, so practice dimensional analysis until it is automatic.

AP-ENVSCI-6-FRQ

U6 FRQ Practice

Master AP Environmental Science Unit 6 free-response questions on energy resources with a step-by-step attack plan, worked calculations, and practice FRQs.

What you'll do in this lesson

A voice-first session with the Crimsora tutor on U6 FRQ Practice, then targeted practice and FRQs — with the tutor adapting to where you get stuck.

Start U6 FRQ Practice free

What this lesson covers

Unit 6 covers energy resources and consumption, and the AP exam loves to test it with free-response questions (FRQs) that mix conceptual explanations with real calculations about power plants, fuel efficiency, and emissions. This lesson is not about re-learning solar panels or fossil fuels — it is about turning what you already know into full-credit FRQ answers.

The three AP Environmental Science FRQ types all appear in energy questions: designing an investigation, analyzing an environmental problem and proposing a solution, and analyzing data. You will practice reading the verbs, showing units in every calculation, and writing answers that earn the point instead of circling it. By the end you will have a repeatable method you can apply on exam day.

The Three FRQ Types and How Energy Shows Up

The AP Environmental Science exam has three free-response questions, each worth 10 points. Recognizing the type tells you what the graders want.

FRQ type	What it asks	Energy example
Designing an Investigation	Identify variables, hypotheses, controls, and data collection	Test how insulation thickness affects heat loss from a home
Analyze an Environmental Problem and Propose a Solution	Describe a problem, its cause, and a realistic fix with justification	Coal plant emissions and a proposed switch to natural gas or wind
Analyze Data	Interpret tables, graphs, and perform calculations	Compare energy output and $CO_2$ per kWh across fuel sources

Energy content fits naturally into all three. A common trap is treating every part as an essay. Instead, match your response to the command verb. Identify and describe need one sentence each; explain and justify require a cause-and-effect chain. The data-analysis FRQ almost always contains at least one multi-step calculation worth 2 to 4 points, so budget time to show your work carefully. Roughly ten minutes per FRQ keeps you on pace across the 70-minute section.

Command Verbs: Say Exactly What the Point Requires

AP FRQs are scored on a rubric where each point maps to a specific task. Under-answering and over-answering both cost you. Learn the verbs.

Verb	What you must do	Length
Identify / State	Name it, no explanation	A phrase
Describe	Give a characteristic or feature	One full sentence
Explain	Give a cause-and-effect or mechanism	One to two sentences with "because"
Calculate	Show the setup, numbers, and units	Show all work
Justify	Give evidence-based reasoning for a claim	One to two sentences
Make a claim / Propose	State a solution or position, then support it	Claim plus support

A frequent misconception is that longer answers earn more. They do not. Graders search for the specific rubric idea, so front-load the exact term. For an energy FRQ asking you to explain why burning coal contributes to climate change, write: "Burning coal releases

CO_2

, a greenhouse gas that absorbs and re-emits infrared radiation, trapping heat in the atmosphere." That one sentence contains the mechanism the rubric wants. Vague phrases like "it causes pollution" earn nothing.

Nailing Energy Calculations

The data-analysis FRQ nearly always includes a calculation, and Unit 6 favors power, energy, and efficiency math. Three rules earn full credit: show the equation or setup, carry units through, and box or clearly state the final answer with correct units.

Key relationships to memorize: power multiplied by time equals energy, so

E = P \times t

. A 1000 MW plant running for one hour produces 1000 MWh. Efficiency is

\text{efficiency} = \frac{\text{useful output}}{\text{total input}} \times 100\%

. Dimensional analysis handles the rest — line up units so unwanted ones cancel.

Remember conversions that appear often: 1 kWh = 1000 Wh, and "kilo" "mega" "giga" step by factors of 1000. When a question gives "barrels per day" or "tons of coal per year," convert to a common time unit first.

The most common error is dropping units mid-calculation, which makes it impossible for graders to award the point even if the number is right. The second most common error is not reading whether the answer should be per year, per day, or per household. Always re-read the final sentence of the prompt before writing your boxed answer. If you make an arithmetic slip but your setup and units are correct, you can still earn most of the calculation points.

Writing Solutions That Earn the Justification Point

The "propose a solution" FRQ is where students lose easy points by being generic. A proposal must be specific, feasible, and tied to the problem, and the justification must explain how the solution reduces the harm.

Weak answer: "Use renewable energy." Strong answer: "Install rooftop solar panels on the town's buildings because solar generates electricity without burning fossil fuels, reducing the

CO_2

emissions that drive climate change." The strong version names the technology, connects it to the specific pollutant or problem, and states the mechanism.

When proposing energy solutions, keep a mental menu tied to Unit 6: energy conservation (better insulation, efficient appliances), fuel switching (coal to natural gas lowers emissions per unit energy), and renewables (solar, wind, hydro, geothermal). Each has trade-offs the exam may ask you to acknowledge — intermittency of wind and solar, habitat impacts of hydro dams, upfront cost of efficiency upgrades.

If the prompt says "describe one economic AND one environmental benefit," answer both parts in separate sentences so the grader can find each point. Splitting compound prompts into clearly labeled pieces is one of the fastest ways to gain points without knowing anything extra.

A Repeatable FRQ Attack Plan

Use the same routine on every energy FRQ. First, read the entire question and underline every command verb and every quantity. Second, note how many points each part is worth — part labels like (a), (b), (c) usually correspond to point clusters. Third, answer in order, restating key terms from the prompt so your response stays on target.

For calculations, write the formula first, substitute numbers with units, then simplify. Never do math in your head; the rubric rewards visible steps. For explanations, use the word "because" to force yourself into cause-and-effect.

Manage time strictly. With three FRQs in 70 minutes, aim for about 22 minutes each with a few minutes to review. If you get stuck on one part, move on — parts are scored independently, so a blank (b) does not prevent you from earning (c). Finally, never leave a proposal or explanation as a single vague clause. One extra specific sentence often converts a near-miss into a scored point. Consistency, not brilliance, wins the FRQ section.

Key terms

Free-Response Question (FRQ).: An open-ended AP exam item scored on a point-based rubric; AP Environmental Science has three, each worth 10 points.
Command Verb.: The action word in a prompt (identify, describe, explain, calculate, justify) that dictates exactly how much and what kind of response earns the point.
Efficiency.: The ratio of useful energy output to total energy input, expressed as $\frac{\text{output}}{\text{input}} \times 100\%$ .
Power vs. Energy.: Power is the rate of energy use (watts); energy is power over time (watt-hours), related by $E = P \times t$ .
Dimensional Analysis.: A method of solving problems by multiplying by conversion factors so units cancel, leaving the desired unit.
Justification.: Evidence-based reasoning that explains why a claim or proposed solution actually works, required for many FRQ points.
kilowatt-hour (kWh).: A unit of energy equal to using one kilowatt of power for one hour; the standard unit for electricity consumption.

Worked example

A coal-fired power plant has a generating capacity of 500 MW and operates at full capacity for 8,000 hours per year. The plant is 35% efficient, and burning coal releases 0.9 kg of

CO_2

per kWh of electricity generated. (a) Calculate the total electrical energy produced in one year, in kWh. (b) Calculate the annual

CO_2

emissions in kilograms. (c) Propose and justify one action to reduce the plant's annual

CO_2

emissions.

Part (a): Start with the energy equation

E = P \times t

. Power is 500 MW, which equals 500,000 kW. Multiply by time:

E = 500{,}000 \text{ kW} \times 8{,}000 \text{ h} = 4{,}000{,}000{,}000 \text{ kWh}

, or

4 \times 10^9

kWh per year. Notice the efficiency value is not needed here because the plant's capacity already describes electrical output, a common distractor.

Part (b): Multiply energy by the emission factor.

4 \times 10^9 \text{ kWh} \times 0.9 \frac{\text{kg } CO_2}{\text{kWh}} = 3.6 \times 10^9 \text{ kg } CO_2

per year. Keep units attached so kWh cancels and kilograms remain.

Part (c): Make a specific claim and justify it. Example: "Retrofit the plant with more efficient turbines and boilers, or co-fire with biomass, because higher efficiency means more electricity is produced per unit of coal burned, lowering the

CO_2

released per kWh." Alternatively, propose replacing part of the output with wind or solar because those sources generate electricity without combustion, eliminating those emissions. Either answer scores because it names a concrete action and connects it to reduced

CO_2

through a stated mechanism.

Practice questions

An FRQ asks you to "explain" why natural gas is often described as a cleaner-burning fossil fuel than coal. Which response would earn the point?

Natural gas is better for the environment.
Natural gas releases less $CO_2$ and fewer particulates per unit of energy because it has a higher hydrogen-to-carbon ratio than coal.
Natural gas is a renewable resource that never runs out.
Natural gas is cheaper than coal in most markets.

Answer: Natural gas releases less $CO_2$ and fewer particulates per unit of energy because it has a higher hydrogen-to-carbon ratio than coal.

The verb "explain" requires a mechanism. The correct choice gives cause and effect (higher hydrogen-to-carbon ratio leads to less

CO_2

per unit energy). The vague choice earns nothing, the "renewable" choice is factually wrong since natural gas is a fossil fuel, and the price statement is economic, not the emissions mechanism asked for.

A household uses a 1,200 W space heater for 5 hours per day. Calculate the energy the heater uses in one 30-day month, in kWh, and show your work.

Answer: $1{,}200 \text{ W} = 1.2 \text{ kW}$ ; $1.2 \text{ kW} \times 5 \frac{\text{h}}{\text{day}} \times 30 \text{ days} = 180 \text{ kWh}$ .

Convert watts to kilowatts first (divide by 1000) so the final answer lands in kWh. Then apply

E = P \times t

with time in hours. Multiplying 1.2 kW by 5 hours gives 6 kWh per day, and 6 times 30 days equals 180 kWh. Always show the conversion and carry units — a correct setup earns partial credit even if arithmetic slips.

For a "designing an investigation" FRQ, a student wants to test how the tilt angle of a solar panel affects its electricity output. Identify the independent variable, the dependent variable, and one variable that should be held constant.

Answer: Independent variable: the tilt angle of the solar panel. Dependent variable: the electricity output (voltage, current, or power) measured. Controlled variable: any of time of day, light intensity, panel type, or temperature.

The independent variable is what the experimenter deliberately changes (tilt angle). The dependent variable is what is measured in response (electrical output). Controlled variables must be held constant so they do not confound the result; keeping light intensity or time of day the same ensures differences in output come from tilt alone. Naming a specific, measurable output earns the point over a vague answer like "how well it works."

FAQ

How much time should I spend on each Unit 6 FRQ?: The free-response section gives 70 minutes for three FRQs, so budget roughly 22 minutes each and leave a few minutes to review calculations and units. If one part stumps you, move on — parts are scored independently.
Do I lose points for wrong arithmetic if my setup is correct?: Usually not all of them. Calculation points are often split between correct setup with units and the correct final value. If your equation, substitution, and units are right but you make a small math error, you typically still earn most of the credit, which is why showing every step matters.
What is the most common reason students lose easy FRQ points on energy questions?: Two things: dropping units in calculations so graders cannot verify the answer, and giving vague proposals like "use renewables" without naming a specific technology and explaining the mechanism that reduces the problem. Specificity and units recover those points.
Do I need to memorize energy formulas for the FRQ section?: Yes. Know $E = P \times t$ , the efficiency formula, and metric prefix conversions (kilo, mega, giga differ by factors of 1000). The exam expects you to set up and complete calculations without a provided equation sheet, so practice dimensional analysis until it is automatic.

Learn this with a teacher, not a page

The Crimsora tutor teaches U6 FRQ Practice live — explaining on a whiteboard, asking you questions, and adapting to where you get stuck.

Try a live session free