IB myp 4-5 Chemistry – Practice Questions- All Topics
Topic :Bonding–energy changes in reactions
Topic :Bonding- Weightage : 21 %
All Questions for Topic :structure and bonding,properties,chemical formulas,chemical reactions and the conservation of mass; balancing,equations, the mole concept and chemical calculations;
reaction kinetics [rates, and factors affecting rates/collision theory],equilibria/reversible reactions,energy changes in reactions, endo- and exothermicity; combustion of fuels)
Question (12 marks) – Hydrogen as an Environmentally Friendly Fuel
a. (2 marks) Hydrogen was discovered by Sir Henry Cavendish in 1766 when he reacted metals with acid. He placed three different metals: zinc, iron and tin into acid. He observed that hydrogen was produced at different rates. Outline why hydrogen was produced at different rates.
▶️ Answer & Explanation
Answer: More reactive metals will produce hydrogen more quickly or higher rates. The metals react differently because they have different reactivities.
Detailed Explanation: The rate of hydrogen production depends on the metal’s position in the reactivity series. Zinc is more reactive than iron, which is more reactive than tin. More reactive metals lose electrons more easily, reacting faster with acids to produce hydrogen gas.
b. (3 marks) Hydrogen is a colourless gas. Even though hydrogen is the most abundant element in the universe, there is not enough in our atmosphere for it to be used as a renewable energy source. When used as an energy source, hydrogen needs to be manufactured. There are several different processes used to manufacture hydrogen. Manufactured hydrogen can be classified into different categories depending on the process used:
| Category of hydrogen | Manufacturing process | Environmental impact |
|---|---|---|
| Grey | Natural gas or methane are combined with steam and broken down. | Carbon monoxide is produced. Carbon monoxide reacts to form carbon dioxide. Carbon dioxide is released into the atmosphere. |
| Blue | Natural gas or methane are combined with steam and broken down. | Carbon monoxide is produced. Carbon monoxide reacts to form carbon dioxide. Carbon dioxide is captured and stored to prevent its release into the atmosphere. |
| Green | Electrolysis of water. | Electrical energy intensive. |
Grey and blue hydrogen are produced in the presence of a nickel catalyst. Explain how a catalyst works in a chemical reaction.
▶️ Answer & Explanation
Answer: Speeds up the rate of reaction. By lowering the activation energy or providing an alternative pathway. Without being used up.
Detailed Explanation: The nickel catalyst provides an alternative reaction pathway with lower activation energy. It forms temporary bonds with reactant molecules (CH4 and H2O), facilitating the reaction while being regenerated at the end.
c. (4 marks) Calculate the number of moles of hydrogen produced when 8.00 kg of methane react with excess water vapour when producing grey and blue hydrogen.
CH4(g) + H2O(g) → CO(g) + 3H2(g)
▶️ Answer & Explanation
Answer: Molar mass of methane = 16 g/mol. 8 kg methane = 500 moles. 1 mole methane produces 3 moles of H2. Moles of hydrogen produced = 1500 mol.
Detailed Solution:
1. Moles of CH4 = 8000g ÷ 16g/mol = 500 mol
2. From stoichiometry: 500 mol CH4 → 1500 mol H2
d. (1 mark) After it is produced, hydrogen must be transported to where it is needed. To allow it to be transported safely, the hydrogen is reacted with nitrogen to form ammonia. Suggest why it is safer to transport ammonia rather than hydrogen.
▶️ Answer & Explanation
Answer: Ammonia is not flammable / Ammonia has a distinct smell so leaks can be detected.
Detailed Explanation: Hydrogen is highly flammable (4-75% explosive range in air) and leaks are hard to detect. Ammonia’s strong odor and higher ignition temperature make it safer for transport.
e. (2 marks) Traditional cement manufacture uses limestone. Carbon dioxide from the blue hydrogen process can be combined with calcium oxide to produce calcium carbonate.
CaO(s) + CO2(g) → CaCO3(s)
State one environmental benefit of using the carbon dioxide in this process. Justify your answer.
▶️ Answer & Explanation
Answer: Carbon dioxide is not released into the atmosphere. The CO2 is utilized instead of being stored underground.
Detailed Explanation: This represents carbon capture and utilization (CCU), converting CO2 into stable calcium carbonate while reducing greenhouse gas emissions.
Question:
How might you prevent the formation of carbon monoxide during the combustion of alkanes?
▶️Answer/Explanation
Ans: Ensure that the combustion reaction has a constant supply of oxygen.