ExpertEasy1 markMultiple Choice
AQA GCSE · Question 03.1 · Chemical changes
This question is about water.
Hydrogen gas reacts with oxygen gas to produce water. Water is decomposed into hydrogen gas and oxygen gas using electricity.
Which of these words describes the reaction between hydrogen and oxygen gas?
This question is about water.
Hydrogen gas reacts with oxygen gas to produce water. Water is decomposed into hydrogen gas and oxygen gas using electricity.
Which of these words describes the reaction between hydrogen and oxygen gas?
Answer options:
A.
Alloying
B.
Combustion
C.
Corrosion
D.
Endothermic
E.
Reversible
How to approach this question
The question asks for two words to describe the reaction of hydrogen and oxygen. This is a "tick two boxes" question, which I have split into two parts. This first part asks for one of the words. Consider the nature of the reaction: hydrogen + oxygen -> water. This is burning. What is the scientific term for burning? Also, does this reaction release or absorb energy?
Full Answer
B.Combustion✓ Correct
The correct answer is Combustion. The reaction of hydrogen with oxygen is burning, which is a combustion reaction. It is also highly exothermic.
The reaction between hydrogen and oxygen (2H₂ + O₂ → 2H₂O) is a highly energetic process.
- **Combustion:** This is the scientific term for burning. Hydrogen is a fuel and it reacts rapidly with oxygen (an oxidant) to release energy.
- **Reversible:** The overall process can be considered reversible because water can be split back into hydrogen and oxygen by electrolysis. The forward reaction (combustion) and the backward reaction (electrolysis) form a reversible process.
- **Exothermic:** The reaction releases a large amount of energy in the form of heat and light, which is the definition of an exothermic reaction. "Endothermic" means a reaction takes in heat.
- **Alloying and Corrosion** are unrelated terms. Alloying is mixing metals, and corrosion is like rusting.
Common mistakes
✗ Confusing combustion with other types of reaction.
✗ Mixing up exothermic and endothermic.
Practice the full AQA GCSE Chemistry Higher Tier Paper 2
48 questions · hints · full answers · grading
More questions from this exam
Q01.1A student investigated an aqueous solution of a salt. The student identified that the salt soluti...EasyQ01.2Describe a test to identify chloride ions. Give the result of the test.EasyQ01.3The student determined the concentration of sodium chloride in the salt solution using this metho...EasyQ01.4How did the student calculate the mass of solid sodium chloride remaining after steps 1 to 5?EasyQ01.5The student calculated the concentration of sodium chloride in the salt solution. Table 1 shows t...Medium