Class 10 › Science Chemical Reactions and Equations Class 10 Science · Chapter 1
Practice all → Summary Questions & answers Practise this chapter → View all Page 1 free about 8 min read , Full kit about 55 min read Page 1 free about 8 min read , Full kit about 55 min read View all 12 amazing Marks Booster kits → Chemical reactions remake substances: bonds in the reactants break and new bonds form, producing products with new properties. A chemical equation is the shorthand for that change, and it must be balanced so that every element has the same number of atoms on both sides — a direct consequence of the law of conservation of mass. Reactions are grouped by what happens to the substances: combination (reactants join into one product), decomposition (one substance splits into many under heat, light or electricity), displacement (a more reactive element pushes out a less reactive one) and double displacement (two compounds exchange ions, often forming a precipitate). Many reactions are redox reactions, where oxidation and reduction happen together. Everyday processes like the rusting of iron (corrosion) and the spoiling of fried food (rancidity) are slow oxidation reactions you can learn to recognise and prevent.
Balanced equation
An equation with equal atoms of each element on both sides.
Combination reaction
Two or more reactants form a single product.
Decomposition reaction
A single reactant breaks into two or more products.
Redox reaction
Oxidation and reduction occurring simultaneously.
Q1 Why must a chemical equation be balanced? Answer Q2 Why is respiration considered an exothermic reaction? Answer Q3 What is a chemical reaction? Give one everyday example. Answer Q4 What information does a balanced chemical equation give? Answer Q5 Define a combination reaction with an example. Answer Q6 What is a decomposition reaction? Name its three types. Answer Q7 Distinguish between displacement and double displacement reactions. Answer Q8 What are oxidation and reduction in terms of oxygen and hydrogen? Answer Q9 What is corrosion, and how can rusting of iron be prevented? Answer Q10 What is rancidity, and how can it be slowed down? Answer Q1 What do you observe? Answer Q1 What do you observe? Answer Q1 Do you observe anything happening around the zinc granules? Answer Q2 Touch the conical flask or test tube. Is there any change in its temperature? Answer Q1 1. Why should a magnesium ribbon be cleaned before burning in air? Answer Q2 2. Write the balanced equation for the following chemical reactions. (i) Hydrogen + Chlorine → Hydrogen chloride Answer Q3 (ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride Answer Q4 (iii) Sodium + Water → Sodium hydroxide + Hydrogen Answer Q5 3. Write a balanced chemical equation with state symbols for the following reactions. (i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride. Answer Q6 (ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water. Answer Q1 Do you feel any change in temperature? Answer Q1 Note the colour of the ferrous sulphate crystals. Answer Q2 Observe the colour of the crystals after heating. Answer Q1 What do you observe? Note down the change, if any. Answer Q1 Is the volume of the gas collected the same in both the test tubes? Answer Q2 What happens in each case? Answer Q3 Which gas is present in each test tube? Answer Q1 What is its colour? Answer Q2 Observe the colour of the silver chloride after some time. Answer Q1 Take about 2 g barium hydroxide in a test tube. Add 1 g of ammonium chloride and mix with the help of a glass rod. Touch the bottom of the test tube with your palm. What do you feel? Is this an exothermic or endothermic reaction? Answer Q1 1. A solution of a substance ‘X’ is used for whitewashing. (i) Name the substance ‘X’ and write its formula. Answer Q2 (ii) Write the reaction of the substance ‘X’ named in (i) above with water. Answer Q3 2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas. Answer Q1 Compare the intensity of the blue colour of copper sulphate solutions in test tubes (A) and (B). Answer Q2 Also, compare the colour of the iron nails dipped in the copper sulphate solution with the one kept aside. Answer Q1 What do you observe? Answer Q1 (i) What was the colour of the precipitate formed? Can you name the compound precipitated? Answer Q2 (ii) Write the balanced chemical equation for this reaction. Answer Q3 (iii) Is this also a double displacement reaction? Answer Q1 What do you observe? Answer Q1 1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Answer Q2 2. Give an example of a double displacement reaction other than the one given in Activity 1.10. Answer Q3 3. Identify the substances that are oxidised and the substances that are reduced in the following reactions. (i) \(4Na(s)+O_2(g)\rightarrow 2Na_2O(s)\) Answer Q4 (ii) \(CuO(s)+H_2(g)\rightarrow Cu(s)+H_2O(l)\) Answer Q1 1. Which of the statements about the reaction below are incorrect? \(2PbO(s)+C(s)\rightarrow 2Pb(s)+CO_2(g)\) (a) Lead is getting reduced. (b) Carbon dioxide is getting oxidised. (c) Carbon is getting oxidised. (d) Lead oxide is getting reduced. (i) (a) and (b) (ii) (a) and (c) (iii) (a), (b) and (c) (iv) all Answer Q2 2. \(Fe_2O_3+2Al\rightarrow Al_2O_3+2Fe\) The above reaction is an example of a (a) combination reaction. (b) double displacement reaction. (c) decomposition reaction. (d) displacement reaction. Answer Q3 3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer. (a) Hydrogen gas and iron chloride are produced. (b) Chlorine gas and iron hydroxide are produced. (c) No reaction takes place. (d) Iron salt and water are produced. Answer Q4 4. What is a balanced chemical equation? Why should chemical equations be balanced? Answer Q5 5. Translate the following statements into chemical equations and then balance them. (a) Hydrogen gas combines with nitrogen to form ammonia. Answer Q6 (b) Hydrogen sulphide gas burns in air to give water and sulpur dioxide. Answer Q7 (c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate. Answer Q8 (d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Answer Q9 6. Balance the following chemical equations. (a) \(HNO_3+Ca(OH)_2\rightarrow Ca(NO_3)_2+H_2O\) Answer Q10 (b) \(NaOH+H_2SO_4\rightarrow Na_2SO_4+H_2O\) Answer Q11 (c) \(NaCl+AgNO_3\rightarrow AgCl+NaNO_3\) Answer Q12 (d) \(BaCl_2+H_2SO_4\rightarrow BaSO_4+HCl\) Answer Q13 7. Write the balanced chemical equations for the following reactions. (a) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water Answer Q14 (b) Zinc + Silver nitrate → Zinc nitrate + Silver Answer Q15 (c) Aluminium + Copper chloride → Aluminium chloride + Copper Answer Q16 (d) Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride Answer Q17 8. Write the balanced chemical equation for the following and identify the type of reaction in each case. (a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s) Answer Q18 (b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g) Answer Q19 (c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g) Answer Q20 (d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g) Answer Q21 9. What does one mean by exothermic and endothermic reactions? Give examples. Answer Q22 10. Why is respiration considered an exothermic reaction? Explain. Answer Q23 11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions. Answer Q24 12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity. Answer Q25 13. What is the difference between displacement and double displacement reactions? Write equations for these reactions. Answer Q26 14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved. Answer Q27 15. What do you mean by a precipitation reaction? Explain by giving examples. Answer Q28 16. Explain the following in terms of gain or loss of oxygen with two examples each. (a) Oxidation Answer Q30 17. A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed. Answer Q31 18. Why do we apply paint on iron articles? Answer Q32 19. Oil and fat containing food items are flushed with nitrogen. Why? Answer Q33 20. Explain the following terms with one example each. (a) Corrosion Answer Q1 Perform the following activity. Take four beakers and label them as A, B, C and D. Put 25 mL of water in A, B and C beakers and copper sulphate solution in beaker D. Measure and record the temperature of each liquid contained in the beakers above. Add two spatulas of potassium sulphate, ammonium nitrate, anhydrous copper sulphate and fine iron fillings to beakers A, B, C and D respectively and stir. Finally measure and record the temperature of each of the mixture above. Find out which reactions are exothermic and which ones are endothermic in nature. Answer
A chemical equation is balanced to satisfy which law?
A Law of multiple proportions B Law of definite proportions C Avogadro’s law D Law of conservation of mass
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