Physical Chemistry - Energetics Practice Questions
A-Levels · A-Level Chemistry · 151 free MCQs with instant results and detailed explanations.
151
Total
49
Easy
79
Medium
23
Hard
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Sample Questions from Physical Chemistry - Energetics
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Q1
Easy
What is the enthalpy change for the reaction when 1 mole of ice melts at 0ยฐC?
A.
0 kJ/mol
B.
6.01 kJ/mol
C.
12.02 kJ/mol
D.
3.34 kJ/mol
Show Answer & Explanation
Correct Answer: B
The enthalpy change for melting ice (the heat of fusion) at 0ยฐC is 6.01 kJ/mol, which is the energy required to convert solid ice to liquid water without changing its temperature.
Q2
Easy
Which of the following statements is true regarding exothermic reactions?
A.
They absorb heat from the surroundings.
B.
They release heat to the surroundings.
C.
They always produce a gas.
D.
They have a positive enthalpy change.
Show Answer & Explanation
Correct Answer: B
Exothermic reactions are characterized by the release of heat to the surroundings, leading to an overall decrease in enthalpy, hence they have a negative enthalpy change.
Q3
Easy
If 100 g of water at 25ยฐC is heated to 75ยฐC, what is the heat absorbed by the water? (Specific heat capacity of water = 4.18 J/gยฐC)
A.
20900 J
B.
2090 J
C.
4180 J
D.
41800 J
Show Answer & Explanation
Correct Answer: A
The heat absorbed can be calculated using the formula q = mcฮT, where m is mass, c is specific heat capacity, and ฮT is the change in temperature. Here, q = 100 g * 4.18 J/gยฐC * (75ยฐC - 25ยฐC) = 20900 J.
Q4
Medium
When 50 g of ice at 0 ยฐC melts into water at 0 ยฐC, how much heat is absorbed? (Given: Heat of fusion of ice = 334 J/g)
A.
16700 J
B.
334 J
C.
1670 J
D.
0 J
Show Answer & Explanation
Correct Answer: A
The heat absorbed when ice melts can be calculated using the formula: Heat = mass ร heat of fusion. Here, Heat = 50 g ร 334 J/g = 16700 J.
Q5
Medium
Which of the following processes is endothermic?
A.
Combustion of propane
B.
Dissolving ammonium nitrate in water
C.
Formation of water from hydrogen and oxygen
D.
Condensation of steam to water
Show Answer & Explanation
Correct Answer: B
Dissolving ammonium nitrate in water is an endothermic process, as it absorbs heat from the surroundings, resulting in a drop in temperature.
Q6
Medium
Calculate the enthalpy change when 2 moles of H2 react with 1 mole of O2 to form water, given that the enthalpy change for the reaction is -286 kJ/mol.
A.
-572 kJ
B.
-286 kJ
C.
0 kJ
D.
572 kJ
Show Answer & Explanation
Correct Answer: A
The total enthalpy change is calculated by multiplying the moles of water produced (2 moles) by the enthalpy change per mole (-286 kJ/mol), yielding -572 kJ.
Q7
Medium
Why is the enthalpy change for the dissolution of sodium chloride in water considered a physical change?
A.
It produces new chemical bonds.
B.
It involves a change in the physical state of the water.
C.
The ions remain in solution without changing their identities.
D.
It releases heat into the surroundings.
Show Answer & Explanation
Correct Answer: C
The dissolution of sodium chloride in water is a physical change because the Na+ and Cl- ions remain intact and do not form new chemical species.
Q8
Hard
The combustion of 1 mole of methane (CH4) releases -890 kJ of heat under standard conditions. If you were to combust 2 moles of methane, how much heat would be released?
A.
-890 kJ
B.
-1780 kJ
C.
-445 kJ
D.
-8900 kJ
Show Answer & Explanation
Correct Answer: B
Combustion reactions are typically proportional to the amount of substance reacted. Since 1 mole of methane releases -890 kJ, combusting 2 moles would release double that amount, which is -890 kJ * 2 = -1780 kJ.
Q9
Hard
A certain reaction has a standard enthalpy change of -150 kJ/mol. If the reaction takes place at constant pressure and produces 3 moles of product, what is the total change in enthalpy for the reaction?
A.
-450 kJ
B.
-150 kJ
C.
150 kJ
D.
0 kJ
Show Answer & Explanation
Correct Answer: A
The standard enthalpy change is given per mole of reaction. Since 3 moles are produced, the total change in enthalpy is -150 kJ/mol * 3 moles = -450 kJ.
Q10
Hard
Consider a calorimetry experiment where 50 g of water at 25ยฐC is mixed with 100 g of copper at 100ยฐC. If the final temperature of the mixture is 30ยฐC, what is the approximate specific heat capacity of copper (in J/gยทยฐC)?
A.
0.385 J/gยทยฐC
B.
0.900 J/gยทยฐC
C.
0.500 J/gยทยฐC
D.
1.250 J/gยทยฐC
Show Answer & Explanation
Correct Answer: B
Using the principle of conservation of energy, heat lost by copper equals heat gained by water. The equation is m_c * c_c * (T_initial_c - T_final) = m_w * c_w * (T_final - T_initial_w). Substituting values leads to the specific heat capacity of copper being approximately 0.900 J/gยทยฐC.
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Physical Chemistry - Energetics โ A-Levels A-Level Chemistry Practice Questions Online
This page contains 151 practice MCQs for the chapter Physical Chemistry - Energetics in A-Levels A-Level Chemistry. The questions are organized by difficulty โ 49 easy, 79 medium, 23 hard โ 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.