IB Diploma Chemistry chapter 4: Reactivity 1: What drives chemical reactions? MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
27 exam-style questions on Reactivity 1: What drives chemical reactions?, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Reactivity 1: What drives chemical reactions? questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. Why is carbon monoxide from incomplete combustion dangerous?
A
it binds to haemoglobin, reducing the ability of the blood to carry oxygen
B
it is the main cause of acid rain
C
it absorbs ultraviolet radiation in the stratosphere
D
it dissolves in the lungs to form carbonic acid
Show answer
Answer: A. CO binds strongly to haemoglobin in place of oxygen, so less oxygen reaches the tissues. It is colourless and odourless, so it is hard to detect.
2. Which statement expresses Hess's law?
A
the enthalpy change is larger for a route with more steps
B
the enthalpy change depends on the activation energy of each step
C
the enthalpy change for a reaction is the same whichever route is taken from the same reactants to the same products
D
the enthalpy change is zero for any reaction at 298 K
Show answer
Answer: C. Enthalpy is a state function: ΔH depends only on the initial and final states, not the pathway. This lets us combine equations to find unknown ΔH values.
3. Which statement about fossil fuels is correct?
A
they are carbon neutral because they come from ancient plants
B
coal releases the least CO2 per kJ of energy produced
C
they are non-renewable, and burning them releases carbon that was locked away for millions of years
D
natural gas produces no carbon dioxide when it burns
Show answer
Answer: C. Fossil fuels form over millions of years, so they are finite; burning them adds long-stored carbon to the atmosphere as CO2. Coal releases the most CO2 per unit energy, natural gas the least.
4. C(s) + O2(g) → CO2(g), ΔH = −394 kJ mol−1. CO(g) + ½O2(g) → CO2(g), ΔH = −283 kJ mol−1. What is ΔH for C(s) + ½O2(g) → CO(g)?
A
+111 kJ mol−1
B
−111 kJ mol−1
C
−677 kJ mol−1
D
+677 kJ mol−1
Show answer
Answer: B. Use the first equation, then reverse the second: −394 + 283 = −111 kJ mol−1. Adding both values without reversing gives −677.
5. 50.0 cm3 of 1.00 mol dm−3 HCl is mixed with 50.0 cm3 of 1.00 mol dm−3 NaOH and the temperature rises by 6.8 °C. What is the enthalpy change of neutralization? (density 1.00 g cm−3; c = 4.18 J g−1 K−1)
A
−28.4 kJ mol−1
B
+56.8 kJ mol−1
C
−56.8 kJ mol−1
D
−2.84 kJ mol−1
Show answer
Answer: C. Q = 100.0 × 4.18 × 6.8 = 2842 J; water formed = 0.0500 mol; ΔH = −2.842 kJ ÷ 0.0500 = −56.8 kJ mol−1. Use the total mass (100 g) and a negative sign because the temperature rose.
6. What is an advantage of a hydrogen fuel cell over burning hydrogen in an engine?
A
it releases more energy per mole of hydrogen than combustion does
B
it does not need a continuous supply of fuel
C
it converts chemical energy directly into electrical energy, so less energy is wasted as heat
D
it can run without any oxidizing agent
Show answer
Answer: C. The overall reaction and ΔH are the same, but the fuel cell skips the heat engine stage, so its efficiency is higher. It still needs a steady supply of hydrogen and oxygen.
7. On an energy profile, the products are drawn at a lower enthalpy than the reactants. Which statement is correct?
A
the reaction is endothermic and the products are more stable
B
the reaction is exothermic and the products are more stable than the reactants
C
the reaction is exothermic and the reactants are more stable than the products
D
ΔH is equal to the activation energy
Show answer
Answer: B. Products lower than reactants means energy is released (ΔH negative), and lower enthalpy means greater stability.
8. 2S(s) + 3O2(g) → 2SO3(g), ΔH = −790 kJ. S(s) + O2(g) → SO2(g), ΔH = −297 kJ. What is ΔH for 2SO2(g) + O2(g) → 2SO3(g)?
A
−493 kJ
B
+196 kJ
C
−1384 kJ
D
−196 kJ
Show answer
Answer: D. Reverse the second equation and double it (+594 kJ), then add the first: −790 + 594 = −196 kJ. Forgetting to double gives −493 kJ.
9. When ammonium nitrate dissolves in water, the temperature of the water falls. Which describes this process?
A
exothermic, ΔH negative
B
exothermic, ΔH positive
C
endothermic, ΔH positive
D
endothermic, ΔH negative
Show answer
Answer: C. The system takes in energy from the surroundings (the water), so the water cools: endothermic, with a positive ΔH.
10. Use bond enthalpies (kJ mol−1: C=C 614, Br–Br 193, C–C 346, C–Br 285) to find ΔH for C2H4(g) + Br2(g) → C2H4Br2(g).
A
+109 kJ mol−1
B
+176 kJ mol−1
C
−109 kJ mol−1
D
−916 kJ mol−1
Show answer
Answer: C. Broken: 614 + 193 = 807. Formed: 346 + 2(285) = 916. ΔH = 807 − 916 = −109 kJ mol−1. The four C–H bonds are unchanged, so they cancel out.
Reactivity 1: What drives chemical reactions?: questions students ask
How many Reactivity 1: What drives chemical reactions? MCQs are there?
27, each with the answer and a short explanation, across 3 topics: R1.1 Measuring enthalpy changes, R1.2 Energy cycles in reactions, R1.3 Energy from fuels. Every chapter test draws ten of them, so you can take it many times.
Is the IB Diploma Chemistry chapter 4 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
