Heat & Thermodynamics for Competitive Exam Preparation

Heat & Thermodynamics

Q. A 1 kg block of metal at 100°C is placed in 2 kg of water at 20°C. If the final temperature is 30°C, what is the specific heat capacity of the metal? (2023)

A. 0.5 J/kg°C
B. 1 J/kg°C
C. 2 J/kg°C
D. 4 J/kg°C

Solution

Using conservation of energy: m1c1(T1 - Tf) = m2c2(Tf - T2), we find c1 = 2 J/kg°C.

Correct Answer: C — 2 J/kg°C

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Q. A 100 g piece of metal at 150°C is placed in 200 g of water at 25°C. What is the final temperature of the system assuming no heat loss? (2019)

A. 30°C
B. 40°C
C. 50°C
D. 60°C

Solution

Using the principle of conservation of energy, we can calculate the final temperature to be 50°C.

Correct Answer: C — 50°C

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Q. A 2 kg object is heated from 20°C to 80°C. If the specific heat capacity is 0.5 J/g°C, how much heat is absorbed? (2019)

A. 60 kJ
B. 80 kJ
C. 100 kJ
D. 120 kJ

Solution

Heat absorbed (Q) = mcΔT = (2000 g)(0.5 J/g°C)(60°C) = 60,000 J = 60 kJ.

Correct Answer: B — 80 kJ

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Q. A 2 kg piece of copper (specific heat = 0.385 J/g°C) is heated from 25°C to 75°C. How much heat is absorbed? (2022)

A. 2000 J
B. 3000 J
C. 4000 J
D. 5000 J

Solution

Q = mcΔT = 2000 g * 0.385 J/g°C * (75°C - 25°C) = 38500 J.

Correct Answer: B — 3000 J

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Q. A 2 kg piece of iron at 150°C is placed in 1 kg of water at 20°C. What will be the final temperature of the system? (Specific heat of iron = 0.45 J/g°C, water = 4.18 J/g°C) (2023)

A. 25°C
B. 30°C
C. 35°C
D. 40°C

Solution

Using heat transfer equations, we find the final temperature to be approximately 35°C.

Correct Answer: C — 35°C

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Q. A 5 kg block of metal is heated from 20°C to 100°C. If the specific heat capacity of the metal is 0.5 J/g°C, how much heat is required? (2023)

A. 2000 J
B. 2500 J
C. 3000 J
D. 3500 J

Solution

Heat (Q) = m * c * ΔT = 5000 g * 0.5 J/g°C * (100°C - 20°C) = 5000 * 0.5 * 80 = 200000 J = 2000 J.

Correct Answer: C — 3000 J

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Q. A gas expands isothermally at 300 K from a volume of 1 m³ to 2 m³. If the pressure of the gas is 100 kPa, what is the work done by the gas during expansion? (2019)

A. 20 kJ
B. 30 kJ
C. 40 kJ
D. 50 kJ

Solution

Work done (W) = PΔV = 100 kPa * (2 m³ - 1 m³) = 100 kPa * 1 m³ = 100 kJ = 20 kJ.

Correct Answer: A — 20 kJ

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Q. If 200 g of water at 80°C is mixed with 300 g of water at 20°C, what will be the final temperature of the mixture? (2019)

A. 30°C
B. 40°C
C. 50°C
D. 60°C

Solution

Using the formula m1c1T1 + m2c2T2 = (m1 + m2)cT, we find T = (200*80 + 300*20) / (200 + 300) = 40°C.

Correct Answer: B — 40°C

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Q. If the boiling point of water is 100°C, what is the corresponding temperature in Kelvin? (2021)

A. 273 K
B. 373 K
C. 400 K
D. 450 K

Solution

Temperature in Kelvin (K) = °C + 273 = 100 + 273 = 373 K.

Correct Answer: B — 373 K

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Q. In an adiabatic process, the temperature of a gas decreases. What happens to its pressure? (2021)

A. Increases
B. Decreases
C. Remains constant
D. Depends on volume

Solution

In an adiabatic process, as the temperature decreases, the pressure also decreases due to the ideal gas law.

Correct Answer: B — Decreases

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Q. What is the change in internal energy of a gas that absorbs 500 J of heat and does 200 J of work on the surroundings? (2023)

A. 300 J
B. 500 J
C. 700 J
D. 900 J

Solution

ΔU = Q - W = 500 J - 200 J = 300 J.

Correct Answer: A — 300 J

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Q. What is the change in internal energy of a gas that absorbs 500 J of heat and does 200 J of work? (2022)

A. 300 J
B. 500 J
C. 700 J
D. 1000 J

Solution

Using the first law of thermodynamics: ΔU = Q - W = 500 J - 200 J = 300 J.

Correct Answer: A — 300 J

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Q. What is the change in internal energy of a system if 500 J of work is done on it and 200 J of heat is lost? (2023)

A. 300 J
B. 500 J
C. 700 J
D. 900 J

Solution

Change in internal energy (ΔU) = Q - W = -200 J - 500 J = -300 J.

Correct Answer: A — 300 J

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Q. What is the latent heat of fusion if 500 g of ice at 0°C absorbs 334,000 J of heat? (2022)

A. 334 J/g
B. 668 J/g
C. 500 J/g
D. 1000 J/g

Solution

Latent heat of fusion (L) = Q / m = 334,000 J / 500 g = 668 J/g.

Correct Answer: A — 334 J/g

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Q. What is the latent heat of fusion of ice if 80 g of ice at 0°C melts to water at 0°C, absorbing 2400 J of heat? (2022)

A. 30 J/g
B. 40 J/g
C. 50 J/g
D. 60 J/g

Solution

Latent heat of fusion (L) = Q/m = 2400 J / 80 g = 30 J/g.

Correct Answer: B — 40 J/g

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Q. What is the specific heat capacity of a substance if 500 J of heat is required to raise the temperature of 2 kg of the substance by 10°C? (2021)

A. 25 J/kg°C
B. 50 J/kg°C
C. 75 J/kg°C
D. 100 J/kg°C

Solution

Specific heat capacity (c) = Q / (m * ΔT) = 500 J / (2 kg * 10°C) = 25 J/kg°C.

Correct Answer: B — 50 J/kg°C

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Q. What is the work done on a gas when it is compressed isothermally from 4 L to 2 L at a pressure of 1 atm? (2021)

A. 2.0 L·atm
B. 4.0 L·atm
C. 6.0 L·atm
D. 8.0 L·atm

Solution

Work done (W) = PΔV = 1 atm * (2 L - 4 L) = 2 L·atm.

Correct Answer: B — 4.0 L·atm

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Heat & Thermodynamics

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