Física - Termodinâmica Practice Questions
ENEM (Brazil) · ENEM Ciências da Natureza · 149 free MCQs with instant results and detailed explanations.
149
Total
51
Easy
78
Medium
20
Hard
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Sample Questions from Física - Termodinâmica
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Q1
Easy
What happens to the pressure of a gas if its volume is reduced while keeping the temperature constant?
A.
Pressure increases
B.
Pressure decreases
C.
Pressure remains the same
D.
Pressure fluctuates
Show Answer & Explanation
Correct Answer: A
According to Boyle's Law, when the volume of a gas decreases at constant temperature, the pressure increases. This is because the gas molecules have less space to move, leading to more frequent collisions with the walls of the container, thus increasing the pressure.
Q2
Easy
Which of the following processes involves a transfer of heat that occurs without a change in the temperature of the substance?
A.
Heating water in a pot
B.
Melting ice
C.
Boiling water
D.
Cooling air in a refrigerator
Show Answer & Explanation
Correct Answer: B
The process of melting ice is an example of a phase change where heat is absorbed (latent heat) without a change in temperature. This means that while ice gets transformed into water, the temperature remains at 0°C until all ice has melted.
Q3
Easy
If a gas is compressed to half its original volume at constant temperature, what happens to its pressure according to the ideal gas law?
A.
It doubles
B.
It quadruples
C.
It remains constant
D.
It halves
Show Answer & Explanation
Correct Answer: A
According to the ideal gas law (PV = nRT), if the volume (V) is halved while keeping the temperature (T) constant, the pressure (P) must double to maintain the equality since the number of moles (n) and the gas constant (R) are unchanged.
Q4
Medium
In a closed system, 100 J of heat is added, and 40 J of work is done by the system. What is the change in internal energy of the system?
A.
60 J
B.
40 J
C.
100 J
D.
140 J
Show Answer & Explanation
Correct Answer: A
According to the first law of thermodynamics, the change in internal energy (ΔU) is equal to heat added (Q) minus work done by the system (W): ΔU = Q - W. Here, ΔU = 100 J - 40 J = 60 J.
Q5
Medium
A gas expands isothermally at a temperature of 300 K, doing 200 J of work. Assuming the ideal gas constant R = 8.31 J/(mol·K), how many moles of gas are involved in this process?
A.
8.06 mol
B.
6.02 mol
C.
2.41 mol
D.
4.82 mol
Show Answer & Explanation
Correct Answer: C
For an isothermal process, the work done (W) is given by W = nRT ln(Vf/Vi). Rearranging gives n = W / (RT ln(Vf/Vi)). The ln term cancels out since we look at a given W, thus n = 200 J / (8.31 J/(mol·K) * 300 K) = 2.41 mol.
Q6
Medium
Which of the following processes is characterized as adiabatic?
A.
Heating a gas in a closed container.
B.
Compressing a gas without heat exchange.
C.
Cooling a gas in contact with a cold reservoir.
D.
Heating water in an open pot on a stove.
Show Answer & Explanation
Correct Answer: B
An adiabatic process is defined as one where no heat is exchanged with the environment. Compressing a gas in a closed system without allowing heat to enter or leave exemplifies this process.
Q7
Medium
A substance undergoes a phase transition at 0°C, absorbing 334 J of heat per gram. What type of phase change is occurring, and what is the total heat absorbed when 5 grams of the substance undergo this change?
A.
Melting; 1670 J
B.
Freezing; 1670 J
C.
Boiling; 1670 J
D.
Condensation; 334 J
Show Answer & Explanation
Correct Answer: A
The process described is melting, where a solid transforms into a liquid at its melting point. The total heat absorbed for 5 grams is calculated as 5 g * 334 J/g = 1670 J.
Q8
Hard
A gas is contained in a cylinder with a movable piston. If the gas does 300 J of work on the piston while absorbing 500 J of heat, what is the change in internal energy of the gas according to the first law of thermodynamics?
A.
200 J
B.
500 J
C.
800 J
D.
300 J
Show Answer & Explanation
Correct Answer: A
According to the first law of thermodynamics, the change in internal energy (ΔU) is given by ΔU = Q - W, where Q is the heat added to the system and W is the work done by the system. Here, Q = 500 J and W = 300 J, thus ΔU = 500 J - 300 J = 200 J.
Q9
Hard
A heat pump operates by transferring heat from a colder area to a warmer area. If a heat pump consumes 2 kWh of electrical energy and transfers 8 kWh of heat energy to a building, what is the coefficient of performance (COP) of the heat pump?
A.
4
B.
2
C.
3
D.
1.5
Show Answer & Explanation
Correct Answer: A
The coefficient of performance (COP) is calculated as the ratio of heat energy output to work input. Here, COP = Heat energy transferred / Work input = 8 kWh / 2 kWh = 4.
Q10
Hard
A gas is contained in a cylinder with a movable piston. If the gas initially occupies a volume of 4.0 L at a pressure of 2.0 atm and is heated until its volume expands to 8.0 L while maintaining constant pressure, what is the final temperature of the gas if the initial temperature was 300 K?
A.
600 K
B.
300 K
C.
900 K
D.
150 K
Show Answer & Explanation
Correct Answer: A
According to Charles's Law, V1/T1 = V2/T2. Rearranging gives us T2 = (V2 * T1) / V1. Substituting the values: T2 = (8.0 L * 300 K) / 4.0 L = 600 K, making option A correct.
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Física - Termodinâmica — ENEM (Brazil) ENEM Ciências da Natureza Practice Questions Online
This page contains 149 practice MCQs for the chapter Física - Termodinâmica in ENEM (Brazil) ENEM Ciências da Natureza. The questions are organized by difficulty — 51 easy, 78 medium, 20 hard — so you can choose the right level for your preparation.
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