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3 X – Science
CHAPTER – 1
q Chemical Reaction : – Whenever a chemical change occurs we can say that a chemical reaction has taken place eg – Food gets digested in our body
q Chemical Equation :– A chemical reaction can be expressed symbolically by using chemical equation
eg magnesium is burnt into air to form magnesium oxide can be represented as
Mg + O 2 → MgO
- We can observe or recognise a chemical reaction by observing change in state, colour, by evolution of gas or by change in temperature.
q Physical state of the reactant and products are mentioned to make chemical reaction more informative. eg we use (g) for gas, (l) for liquid, (s) for solid and (aq) for aqueous.
q Balancing Equation :– We balance the chemical equation so that no. of atoms of each element involved in the reaction remain same at the reactant and product side. eg Fe + H 2 O → Fe 2 O 3 + H 2 can be written as 3 Fe(s) + 4H 2 O(g) (^) → Fe 2 O 3 (s) +4H 2 (g)
q Combination Reaction :– The reaction in which two or more substances combine to form a new single substance
Chemical Reactions and Equations
4 X – Science
eg CaO(s) + H 2 O( l ) →^ Ca(OH)2 (aq) Calcium Water Calcium hydroxide oxide (slaked lime) Quick lime
- Ca(OH) 2 slaked lime is used for white washing walls. It reacts will CO 2 to form CaCO 3 and gives a shiny finish to the walls.
Ca(OH) 2 (aq)+^
CO 2
(g)
→ (^) CaCO 3 (s)+^ H 2 O ( l )
Calcium Calcium
hydroxide Carbonate
C(s) + O2(g) →^ CO2(g) + heat + light
2H2(g) + O2(g) →^ 2H 2 O( l )
q Exothermic Reactions :– Reaction in which heat is released along with the formation of products.
eg. CH4(g) + 2O2(g) →^ CO2(g) + 2H 2 O(g)
- Respiration is also exothermic reaction.
- De composition of vegetable matter into compost.
q De compositon Reactions :– The reaction in which a single substance decomposes to give two or more substances. De composition reactions can be of three types Thermal Decompositon :– When a decompositon reaction is carried out by heating
6 X – Science
- Endothermic Reactions – The reactions which require energy in the form of heat, light or electricty are called Endothermic Reactions.
2Ba(OH) 2 + NH 4 Cl →^ 2BaCl 2 + NH 4 OH
- Displacement Reaction : The chemical Reaction in which an element displaces another element from its solution
Fe(s) + CuSO4(aq) →^ FeSO 4 + Cu(s) Copper (aq) Sulphate Iron Sulphate
- The nail becomes brownish in colour and the blue colour of Copper Sulphate solution fade.
- Other examples Zn(s) + CuSO 4 →^ ZnSO 4 + Cu(s) (aq) (aq) Copper Zinc Sulphate Sulphate
Pb(s) + CuCl 2 →^ PbCl 2 + Cu(s) (aq) (aq) Copper Lead Chloride Chloride
- Zinc and lead are more reactive elements than copper. They displace copper from its compounds.
7 X – Science
- Double Displacement Reaction : The reaction in which two different atoms or group of atoms are mutually exchanged
eg. Na 2 SO 4 + BaCl 2 →^ BaSO4(s) + 2NaCl (aq) (aq) (aq) Sodium Barium Barium Sodium Sulphate Chloride Sulphate Chloride A white substance is formed due to above reaction. The insoluble substance is called precipitate. Precipitation Reaction – Any reaction that produces a precipitate is called a precipitation reaction. eg. Pb(NO 3 ) 2 + 2KI →^ PbI 2 +2KNO 3 (aq) (aq) (aq) Lead Nitrate Potassium Lead Potassium Iodide Iodide Nitrate
- Oxidation : Oxidation is the gain of oxygen or loss of hydrogen
eg. 2Cu + O 2 Heat^ → 2CuO
When Copper is heated a black colour appears. If this CuO is reacted with hydrogen gas then again Cu becomes brown as reverse reaction takes place CuO + H 2 Heat^ → Cu + H 2 O
- Reduction : Reduction is the loss of oxygen or gain of hydrogen.
- Redox Reaction : The reaction in which one reactant gets oxidised while other gets reduced
eg. ZnO + C →^ Zn + CO MnO 2 + 4HCl →^ MnCl 2 + 2H 2 O + Cl 2
9 X – Science
Answer the following questions briefly (2 mark)
- Write down the observations which indicate the occurence of a chemical reaction.
- Why is respiration considered as an exothermic reaction? Explain.
- Transfer the following statements into Chemical equations and then balance them. a) Hydrogen gas combines with nitrogen to form ammonia. b) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
- Identify the substances that are oxidised and the substances that are reduced to the folllowing reactions.
- Na + O 2 →^ Na 2 O (s) (g) (s) CuO + H 2 →^ Cu + H 2 O( l ) (s) (g) (s)
- What happens when silver chloride is exposed to sunlight? Give one practical application of this reaction. Write the equation also.
- Why is the bag used for potato chips flushed with nitrogen gas?
Answer the following questions in detail (3 marks)
- Write down the balanced chemical equations for the following reactions.
a) Zinc Carbonate(s) →^ Zinc Oxide + Carbon Dioxide(g) b) Aluminium(s) + Chlorine(g) →^ Aluminium Chloride(s) c) Magnesium(s)+ Water( l ) Heat^ →Magnesium Hydroxide( l )+ Hydrogen(g)
- Choose combination, displacement and double displacement reactions out of the given reactions.
i) MnO 2 (s)
- 4HCl( l ) →^ MnCl 2 (s)
- Cl 2 (g)
+ 2H 2 O
( l ) ii) CaO (s)
+ CO 2
(g)
→ (^) CaCO 3 (s) iii) 2AgCl(s) →^ 2Ag(s) + Cl 2 (g)
10 X – Science
- What happens when CO 2 (g) is passed through slaked lime? Write the balanced chemical equation. Write the type of reaction that has occured.
Explain the following questions detail (5 marks)
- Balance the following chemical equation and identify the type of reaction they represent
KClO 3 →^ KCl + O 2
NH 3 + O 2 →^ NO + H 2 O
Na 2 O + H 2 O →^ NaOH
Na + H 2 O →^ NaOH + H 2
FeCl 3 + NaOH →^ Fe (OH) 3 + NaCl.
- Define various types of chemical reactions. Write one chemical equation for each type.
