Heat & Thermodynamics
Q. What is the change in internal energy of a gas that absorbs 300 J of heat and does 100 J of work on the surroundings? (2020)
A.
200 J
B.
300 J
C.
400 J
D.
500 J
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Solution
Change in internal energy (ΔU) = Q - W = 300 J - 100 J = 200 J.
Correct Answer: A — 200 J
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Q. What is the change in internal energy of a system if 200 J of heat is added and 50 J of work is done by the system?
A.
150 J
B.
250 J
C.
200 J
D.
100 J
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Solution
Using the first law of thermodynamics, ΔU = Q - W = 200 J - 50 J = 150 J.
Correct Answer: A — 150 J
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Q. What is the change in internal energy of a system if 300 J of heat is added and 100 J of work is done by the system? (2021)
A.
200 J
B.
300 J
C.
400 J
D.
500 J
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Solution
Using the first law of thermodynamics: ΔU = Q - W = 300 J - 100 J = 200 J.
Correct Answer: A — 200 J
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Q. What is the efficiency of a Carnot engine operating between 300 K and 600 K? (2022)
A.
0.5
B.
0.33
C.
0.25
D.
0.67
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Solution
Efficiency = 1 - (T_c/T_h) = 1 - (300/600) = 0.5.
Correct Answer: A — 0.5
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Q. What is the efficiency of a Carnot engine operating between 500 K and 300 K? (2022)
A.
0.4
B.
0.5
C.
0.6
D.
0.7
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Solution
Efficiency = 1 - (T2/T1) = 1 - (300/500) = 0.4 or 40%.
Correct Answer: C — 0.6
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Q. What is the efficiency of a Carnot engine operating between a hot reservoir at 600 K and a cold reservoir at 300 K?
A.
0.5
B.
0.33
C.
0.25
D.
0.75
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Solution
Efficiency (η) = 1 - (T_c/T_h) = 1 - (300/600) = 0.5 or 50%.
Correct Answer: B — 0.33
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Q. What is the efficiency of a Carnot engine operating between temperatures of 500 K and 300 K?
A.
0.4
B.
0.5
C.
0.6
D.
0.7
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Solution
Efficiency (η) = 1 - (T2/T1) = 1 - (300/500) = 0.4 or 40%.
Correct Answer: C — 0.6
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Q. What is the final temperature when 200 g of ice at 0°C is added to 100 g of water at 80°C? (Specific heat of water = 4.2 J/g°C) (2020)
A.
0°C
B.
20°C
C.
40°C
D.
80°C
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Solution
Using the principle of conservation of energy, the heat lost by water equals the heat gained by ice. Solving gives a final temperature of 20°C.
Correct Answer: B — 20°C
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Q. What is the final temperature when 200 g of ice at 0°C is added to 100 g of water at 80°C? (Assume no heat loss to the surroundings) (2023)
A.
0°C
B.
20°C
C.
40°C
D.
80°C
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Solution
Using heat balance: m_ice * L_f + m_water * c * (T_final - 80) = 0. Solving gives T_final = 20°C.
Correct Answer: B — 20°C
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Q. What is the heat required to raise the temperature of 2 kg of aluminum from 25°C to 75°C? (Specific heat of aluminum = 0.9 J/g°C) (2022)
A.
9000 J
B.
18000 J
C.
36000 J
D.
4500 J
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Solution
Heat required Q = mcΔT = (2000 g)(0.9 J/g°C)(50°C) = 90000 J.
Correct Answer: B — 18000 J
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Q. What is the latent heat of fusion of ice if 80 calories are required to melt 20 grams of ice? (2020)
A.
40 cal/g
B.
60 cal/g
C.
80 cal/g
D.
100 cal/g
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Solution
Latent heat of fusion (L_f) = Q / m = 80 cal / 20 g = 4 cal/g.
Correct Answer: C — 80 cal/g
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Q. What is the latent heat of vaporization of water if 540 J of energy is required to convert 100 g of water at 100°C to steam? (2021)
A.
540 J/g
B.
54 J/g
C.
5.4 J/g
D.
0.54 J/g
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Solution
Latent heat of vaporization (L) = Q/m = 540 J / 100 g = 5.4 J/g.
Correct Answer: A — 540 J/g
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Q. What is the specific heat capacity of a substance if it requires 500 J to raise the temperature of 2 kg of the substance by 5°C? (2021)
A.
20 J/kg°C
B.
50 J/kg°C
C.
100 J/kg°C
D.
200 J/kg°C
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Solution
Specific heat capacity (c) = Q / (m * ΔT) = 500 J / (2 kg * 5°C) = 50 J/kg°C.
Correct Answer: B — 50 J/kg°C
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Q. What is the specific heat capacity of a substance if it takes 500 J to raise the temperature of 2 kg of the substance by 5°C? (2021)
A.
20 J/kg°C
B.
50 J/kg°C
C.
100 J/kg°C
D.
200 J/kg°C
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Solution
Specific heat capacity (c) = Q / (m * ΔT) = 500 J / (2 kg * 5°C) = 50 J/kg°C
Correct Answer: B — 50 J/kg°C
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Q. What is the specific heat capacity of water if it takes 4200 J to raise the temperature of 1 kg of water by 1°C? (2021)
A.
2100 J/kg°C
B.
4200 J/kg°C
C.
8400 J/kg°C
D.
1000 J/kg°C
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Solution
The specific heat capacity of water is defined as the amount of heat required to raise the temperature of 1 kg of water by 1°C, which is given as 4200 J/kg°C.
Correct Answer: B — 4200 J/kg°C
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Q. What is the temperature in Celsius if the temperature in Kelvin is 273 K?
A.
0°C
B.
100°C
C.
-273°C
D.
273°C
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Solution
To convert Kelvin to Celsius, use the formula: °C = K - 273. Therefore, 273 K - 273 = 0°C.
Correct Answer: A — 0°C
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Q. What is the temperature of a gas in Kelvin if its temperature in Celsius is 25°C? (2019)
A.
273 K
B.
298 K
C.
310 K
D.
325 K
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Solution
Temperature in Kelvin (K) = Temperature in Celsius (°C) + 273.15 = 25 + 273.15 = 298.15 K.
Correct Answer: B — 298 K
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Q. What is the thermal conductivity of a material if a 1 m² area of it conducts 100 J of heat in 10 seconds with a temperature difference of 20°C?
A.
2 W/m°C
B.
5 W/m°C
C.
10 W/m°C
D.
20 W/m°C
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Solution
Using the formula Q = kA(T1-T2)t, we find k = Q / (A(T1-T2)t) = 100 J / (1 m² * 20°C * 10 s) = 0.5 W/m°C.
Correct Answer: B — 5 W/m°C
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Q. What is the work done by an ideal gas during an isobaric expansion if it expands from 2 L to 5 L at a pressure of 3 atm? (2022)
A.
9 J
B.
12 J
C.
15 J
D.
18 J
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Solution
Work done (W) = P * ΔV = 3 atm * (5 L - 2 L) = 3 atm * 3 L = 9 atm·L = 15 J (1 atm·L = 101.325 J)
Correct Answer: C — 15 J
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Q. What is the work done on a gas when it is compressed from 4 L to 2 L at a constant pressure of 2 atm?
A.
4 L·atm
B.
2 L·atm
C.
8 L·atm
D.
0 L·atm
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Solution
Work done (W) = P * ΔV = 2 atm * (2 L - 4 L) = 2 atm * (-2 L) = -4 L·atm (work done on the gas is positive).
Correct Answer: A — 4 L·atm
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Q. What is the work done on a gas when it is compressed from 5 L to 2 L at a constant pressure of 200 kPa? (2022)
A.
600 J
B.
800 J
C.
1000 J
D.
1200 J
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Solution
Work done (W) = P * ΔV = 200 kPa * (2 L - 5 L) = 200 kPa * (-3 L) = -600 J (work done on the gas).
Correct Answer: C — 1000 J
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Q. What is the work done when 1 mole of an ideal gas expands isothermally from 10 L to 20 L at 300 K? (2022)
A.
300 J
B.
600 J
C.
150 J
D.
0 J
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Solution
Work done W = nRT ln(Vf/Vi) = 1 * 8.314 * 300 * ln(20/10) = 600 J.
Correct Answer: B — 600 J
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Q. What is the work done when 1 mole of an ideal gas expands isothermally from 10 L to 20 L at 300 K? (R = 8.31 J/mol·K) (2023)
A.
0 J
B.
830 J
C.
1660 J
D.
2490 J
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Solution
Work done = nRT ln(Vf/Vi) = 1 mol × 8.31 J/mol·K × 300 K × ln(20/10) = 1660 J.
Correct Answer: C — 1660 J
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Q. Which of the following statements is true regarding thermal conductivity? (2023)
A.
It is higher in gases than in solids
B.
It is a measure of a material's ability to conduct heat
C.
It increases with temperature
D.
It is independent of material properties
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Solution
Thermal conductivity is a measure of a material's ability to conduct heat; it varies with material and temperature.
Correct Answer: B — It is a measure of a material's ability to conduct heat
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