Class 9 Chemical Changes and Reactions Mock Test (ICSE)

Topics in Chemical Changes and Reactions

• Conditions for chemical change
• Types of chemical reactions
• Energy changes: exothermic and endothermic reactions
• Photochemical and electrochemical reactions

Chemical Changes and Reactions practice questions with answers

1. Q1Multiple choice·1 mark
   Which of the following is an example of a thermal decomposition reaction?

   1. (a)$\text{Zn (s)} + \text{H}_2\text{SO}_4\text{ (aq)} \rightarrow \text{ZnSO}_4\text{ (aq)} + \text{H}_2\text{ (g)}$
   2. (b)$\text{NaOH (aq)} + \text{HCl (aq)} \rightarrow \text{NaCl (aq)} + \text{H}_2\text{O (l)}$
   3. (c)$\text{2Mg (s)} + \text{O}_2\text{ (g)} \rightarrow \text{2MgO (s)}$
   4. (d)$\text{CaCO}_3\text{ (s)} \xrightarrow{\Delta} \text{CaO (s)} + \text{CO}_2\text{ (g)}$
   Show answer and step marks

   1. Correct option: (d)+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   Which of the following processes is an endothermic reaction?

   1. (a)Respiration in living organisms
   2. (b)Thermal decomposition of limestone
   3. (c)Dissolution of concentrated $\text{H}_2\text{SO}_4$ in water
   4. (d)Burning of natural gas
   Show answer and step marks

   1. Correct option: (b)+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   What condition is essential for a chemical reaction between solid lead nitrate and solid potassium iodide to take place rapidly without heating?

   1. (a)Exposure to sunlight
   2. (b)Passing an electric spark
   3. (c)Adding a catalyst
   4. (d)Dissolving both in water
   Show answer and step marks

   1. Correct option: (d) Dissolving both in water+1

   Answer: (d)
4. Q4Short answer·2 marks
   Give a balanced chemical equation for the displacement reaction between iron metal and copper sulphate solution. State the observation made during this reaction.
   Show answer and step marks

   1. Balanced chemical equation: $\text{Fe (s)} + \text{CuSO}_4\text{ (aq)} \rightarrow \text{FeSO}_4\text{ (aq)} + \text{Cu (s)}$+1
   2. Observation, any one of: the blue colour of the copper sulphate solution fades and turns pale green; a reddish-brown coating of copper forms on the iron; or any other valid observation of this reaction.+1

   Answer: $\text{Fe (s)} + \text{CuSO}_4\text{ (aq)} \rightarrow \text{FeSO}_4\text{ (aq)} + \text{Cu (s)}$; observation (either earns the mark): the blue solution turns pale green, or a reddish-brown coating of copper forms on the iron.
5. Q5Short answer·2 marks
   Define a single displacement reaction and give one balanced chemical equation where an active metal displaces hydrogen from a dilute acid, including state symbols.
   Show answer and step marks

   1. Definition: a single displacement reaction is one in which a more reactive element displaces a less reactive element from its compound (in solution or in an acid).+1
   2. Balanced equation with state symbols, any one of: $\text{Zn (s)} + \text{H}_2\text{SO}_4\text{ (aq)} \rightarrow \text{ZnSO}_4\text{ (aq)} + \text{H}_2\text{ (g)}$; $\text{Zn (s)} + 2\text{HCl (aq)} \rightarrow \text{ZnCl}_2\text{ (aq)} + \text{H}_2\text{ (g)}$; $\text{Mg (s)} + 2\text{HCl (aq)} \rightarrow \text{MgCl}_2\text{ (aq)} + \text{H}_2\text{ (g)}$; or any other valid balanced equation of an active metal with a dilute acid.+1

   Answer: A single displacement reaction is one in which a more reactive element displaces a less reactive element from its compound; e.g. $\text{Zn (s)} + \text{H}_2\text{SO}_4\text{ (aq)} \rightarrow \text{ZnSO}_4\text{ (aq)} + \text{H}_2\text{ (g)}$.
6. Q6Long answer·4 marks
   Answer the following questions based on energy changes in chemical reactions: (a) State the main difference between an exothermic reaction and an endothermic reaction in terms of heat. (b) Give a balanced chemical equation for any one exothermic reaction, including proper state symbols. (c) When quicklime is added to water, the container becomes noticeably hot. (i) Identify whether this reaction is exothermic or endothermic. (ii) Write the balanced chemical equation for the reaction between quicklime and water, including physical state symbols.
   Show answer and step marks

   1. (a) Exothermic reactions release (evolve) heat to the surroundings, whereas endothermic reactions absorb heat from the surroundings.+1
   2. (b) A balanced exothermic equation with state symbols, any one of: $\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + \text{heat}$; $\text{CH}_4\text{(g)} + 2\text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + 2\text{H}_2\text{O(l)} + \text{heat}$; $2\text{Mg(s)} + \text{O}_2\text{(g)} \rightarrow 2\text{MgO(s)} + \text{heat}$; or any other valid balanced exothermic equation with state symbols.+1
   3. (c)(i) Exothermic reaction.+1
   4. (c)(ii) $\text{CaO(s)} + \text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(aq)} + \text{heat}$ (also credit $\text{Ca(OH)}_2\text{(s)}$).+1

   Answer: (a) Exothermic reactions release heat to the surroundings; endothermic reactions absorb heat from them. (b) e.g. $\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)} + \text{heat}$ (any valid balanced exothermic equation with state symbols). (c)(i) Exothermic. (c)(ii) $\text{CaO(s)} + \text{H}_2\text{O(l)} \rightarrow \text{Ca(OH)}_2\text{(aq)} + \text{heat}$ ($\text{Ca(OH)}_2$ as (s) also accepted).

More Class 9 Chemistry mock tests