Energetics and Thermochemistry Practice Questions
IB (International Baccalaureate) · IB Chemistry HL · 151 free MCQs with instant results and detailed explanations.
151
Total
49
Easy
79
Medium
23
Hard
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Sample Questions from Energetics and Thermochemistry
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Q1
Easy
Which of the following statements best describes the enthalpy change for a reaction at constant pressure?
A.
It is equal to the heat absorbed or released during the reaction.
B.
It can be determined by measuring the temperature change of the surroundings.
C.
It is always negative for exothermic reactions.
D.
It is the same as the change in internal energy of the system.
Show Answer & Explanation
Correct Answer: A
The enthalpy change for a reaction at constant pressure is defined as the heat absorbed or released during the reaction, making option A the correct choice.
Q2
Easy
In a calorimetry experiment, 50 g of water at 25°C absorbs 4200 J of heat. What is the final temperature of the water? (Assume no heat losses and specific heat capacity of water is 4.18 J/g°C)
A.
25.5°C
B.
26.0°C
C.
27.0°C
D.
28.0°C
Show Answer & Explanation
Correct Answer: B
Using the formula q = mcΔT, where q is heat absorbed, m is mass, c is specific heat capacity, and ΔT is the change in temperature, we find ΔT = q/(mc) = 4200/(50 * 4.18) = 20.1°C. Therefore, the final temperature is 25°C + 20.1°C = 26.0°C.
Q3
Easy
Which process is considered exothermic?
A.
Dissolving ammonium nitrate in water.
B.
Combustion of methane.
C.
Melting of ice.
D.
Sublimation of dry ice.
Show Answer & Explanation
Correct Answer: B
The combustion of methane releases heat to the surroundings, making it an exothermic process. In contrast, the other processes either absorb heat or are endothermic.
Q4
Medium
Which of the following statements about enthalpy changes is correct?
A.
Enthalpy change is the heat content of a system at constant pressure.
B.
Enthalpy change can be negative only when a reaction absorbs heat.
C.
Enthalpy change is independent of the reaction pathway.
D.
Enthalpy change is measured in joules per mole.
Show Answer & Explanation
Correct Answer: A
Enthalpy change refers to the heat absorbed or released by a system at constant pressure, making option A correct. Options B and C contain inaccuracies about heat absorption and reaction pathways respectively, while D is vague as enthalpy is often measured in kJ/mol.
Q5
Medium
A reaction has an enthalpy change of -150 kJ/mol. What type of reaction is it?
A.
Endothermic
B.
Exothermic
C.
Isothermal
D.
Isochoric
Show Answer & Explanation
Correct Answer: B
An enthalpy change of -150 kJ/mol indicates that the reaction releases heat, classifying it as an exothermic reaction. Endothermic would mean heat is absorbed, while isothermal and isochoric are not related to enthalpy changes.
Q6
Medium
When 50 g of water at 25 °C is heated to 75 °C, what is the change in thermal energy? (Specific heat capacity of water = 4.18 J/g°C)
A.
1045 J
B.
1040 J
C.
840 J
D.
2100 J
Show Answer & Explanation
Correct Answer: A
The formula Q = mcΔT gives us the change in thermal energy. Here, m = 50 g, c = 4.18 J/g°C, and ΔT = 75°C - 25°C = 50°C. Thus, Q = 50 * 4.18 * 50 = 1045 J.
Q7
Medium
Which of the following is a direct consequence of the first law of thermodynamics?
A.
Energy can be created from nothing.
B.
The total energy of an isolated system is constant.
C.
Heat can be converted completely into work.
D.
All processes are reversible.
Show Answer & Explanation
Correct Answer: B
The first law of thermodynamics states that energy cannot be created or destroyed, which means the total energy of an isolated system remains constant. Options A, C, and D are incorrect interpretations of this law.
Q8
Hard
A 50.0 g sample of water is heated from 25.0 °C to 75.0 °C. What is the amount of heat energy absorbed by the water? (Specific heat capacity of water = 4.18 J/g°C)
A.
1045 J
B.
2100 J
C.
524 J
D.
5000 J
Show Answer & Explanation
Correct Answer: A
The heat absorbed (q) can be calculated using the formula q = mcΔT, where m is mass, c is specific heat capacity, and ΔT is the change in temperature. Here, m = 50.0 g, c = 4.18 J/g°C, and ΔT = 75.0 °C - 25.0 °C = 50.0 °C. Thus, q = 50.0 g * 4.18 J/g°C * 50.0 °C = 1045 J.
Q9
Hard
The enthalpy change for the reaction 2H2(g) + O2(g) → 2H2O(g) is -483.6 kJ. If the reaction is reversed, what will be the enthalpy change for the reverse reaction?
A.
-483.6 kJ
B.
0 kJ
C.
483.6 kJ
D.
-241.8 kJ
Show Answer & Explanation
Correct Answer: C
When a reaction is reversed, the sign of the enthalpy change is also reversed. Therefore, the enthalpy change for the reverse reaction will be +483.6 kJ, as it is the opposite of -483.6 kJ.
Q10
Hard
The enthalpy change for the formation of water from hydrogen and oxygen gases at standard conditions is -286 kJ/mol. What is the enthalpy change for the formation of 2 moles of water?
A.
-572 kJ
B.
-143 kJ
C.
-572 J
D.
-286 kJ
Show Answer & Explanation
Correct Answer: A
The enthalpy change for the formation of water is given as -286 kJ/mol. Therefore, for 2 moles, the enthalpy change will be twice that value: -286 kJ/mol × 2 mol = -572 kJ.
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Energetics and Thermochemistry — IB (International Baccalaureate) IB Chemistry HL Practice Questions Online
This page contains 151 practice MCQs for the chapter Energetics and Thermochemistry in IB (International Baccalaureate) IB Chemistry HL. The questions are organized by difficulty — 49 easy, 79 medium, 23 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit.