Chemical Reactions and Equations ,class 10th

Chemical Reactions And Equations For Class 10th 

Chemical Reactions And Equations: 

Balnced and unblanced chemical equations and balancing of cemical equatons.

Chemical Reaction:

The transformation of chemical substance into another chemical subsubstance is known as Chemical Reaction. For example: Rusting of iron, setting of milk into curd, digestion of food, respiration, etc.

In chemical reaction, new substance is formed which is completely different in properties from the original substance, so in a chemical reaction, chemical change takes place.

Only a rearrangement of atoms takes place in a chemical reaction.

(1) The substances which take part in a chemical reaction are called reactants.

(2) The new substances produced as a result of chemical reaction are called products.

Example: The burning of magnesium in air to form magnesium oxide is an example of chemical reaction.

    2Mg(s) + O2(g) ----> 2MgO(s)

Before burning in air, the magnesium ribbon is cleaned by rubbing with sand paper.

This is done to remove the protective layer of basicbasic magnesium carbonate from the surface of magnesium ribbon.

•Reactant: Substances which take part in a chemical reaction are called reactants. Example: Mg and O2.

•Products: New substances formed after a chemical reaction are called product. Ex: MgO.

Characterstics of Chemical Reactions:

(1) Evolution of gas: The chemical reaction between zinc and dilute sulphuric acid is characterised by the evolution of gas.

   Zn(s) + H2SO4(aq) ----> ZnSO4(aq)                                                 + H2(g)

(2) Change in colour: The chemical chemical reaction between citric acid and purple coloured potassium permanganate solution is characterised by a change in colour from purple to colourless.

The chemical reaction between sulphur dioxide gas and acidified potassium dichromate solution is characterised by a change in colour from orange to green.

(3) Change in state of substance: The combustion reaction of candle wax is characterised by a change in state from solid to liquid and gas (because wax is solid, water formed by the combustion of wax is a liquid at room tempreture whereas, carbon dioxide produced by the combustion of wax is a gas). There are some chemical reactions which can show more than one characteristics.

(4) Change in temperature: The chemical reaction between quick lime water to form slaked lime is characterised by a change in temperatue (which is rise in temperature).

The chemical reaction between zinc granules and dilute sulphuric acid is also characterised by change in temperature (which is rise in temperature).

(5) Formation of precipitate: The chemical reaction between sulphuric acid and barium chloride solution is characterised by the formation of a white precipitate of barium sulphate.

   BaCl2(aq) + H2SO4(aq) ----->                                      BaSO4(s) + 2HCl(aq) 

                            (ppt)

Some important Questions Of Chapter Chemical Reaction And Equations

1. Give 5 examples each of physical and chemical changes that take place around us in our day to day life.

2. When a magnesium ribbon is burnt in air, what are the two observations that you make?

3. Write a balanced chemical equation to represent decomposition of lead nitrate on heating. What are brown fumes due to?

4. Make a list of at least 10 cations and 10 anions.

5. Taking help from the list prepared in Q4,, write the chemical formulae of:-

  (i) Barium chloride (ii) Sodium Sulphate (iii) Ammonium phosphate (iv) Calcium hydroxide

  (v) Aluminium carbonate (vi) Magnesium hydrogen carbonate (vii) Zinc sulphide

  (viii) copper (׀) chloride (ix) Potassium Bromide (x) Lead nitrate (xi) Iron ( ׀׀׀) oxide (xii) Sodium Oxide (xiii) Silver sulphide (xiv) Calcium Fluoride

6. Write the following in the form of balanced chemical equations:-

  (a) Calcium carbonate decomposes on heating to form calcium oxide and carbon – di – oxide.

  (b) When ammonium hydroxide is added to a solvent of iron (ll) Sulphate, a green ppt of iron (ll) hydroxide and ammonium Sulphate are formed.

  (c) When a nail of iron is added to a solution of copper Sulphate, iron (ll) Sulphate and copper metal are formed.

  (d) Zinc reacts with dil hydrochloric acid to form zinc chloride and hydrogen gas is liberated.

7. A chemical reaction which is both combination as well as exothermic, is used by us for white washing purposes. Write the equation for the same.

8. What is a decomposition reaction? Give 2 examples each of decomposition taking place due to heat, light and electricity.

9. How does a displacement reaction differ from a double displacement reaction? Give examples to explain.

Some definitions of this chapter

Top definitions:

1. Chemical reaction: A chemical reaction involves a chemical change in which substances react to form new substances with entirely new properties. Substances that react or take part in the reaction are known as reactants and the substances formed are known as products. 

2. Physical change: If a change involves change in colour or state but no new substance is formed, then it is a physical change.

3. Chemical change: If a change involves formation of new substances, it is a chemical change.

4. Chemical equation: The symbolic representation of a chemical reaction is called a chemical equation.

5. Exothermic and endothermic reactions: If heat is evolved during a reaction, then such a reaction is known as exothermic reaction. If heat is absorbed from the surroundings, then such a reaction is known as endothermic reaction

6. Combination reaction: Combination reaction is a reaction in which 2 or more substances combine to give a single product.

7. Decomposition reaction: In a decomposition reaction, a single reactant decomposes to give 2 or more products. Decomposition reactions require energy in the form of heat, light or electricity

8. Displacement reaction: A reaction in which a more active element displaces less active element from its salt solution.

9. Reactivity series: The Reactivity series is a list of metals arranged in the order of decreasing reactivity. The most reactive metal is placed at the top and the least reactive metal is placed at the bottom.

10.Double displacement reaction: A chemical reaction in which there is an exchange of ions between the reactants to give new substances is called a double displacement reaction.

11.Precipitation reaction: An insoluble solid known as precipitate is formed during a double displacement reaction. Such reactions are also known as precipitation reactions.

12.Redox reaction: A reaction, in which oxidation and reduction takes place simultaneously is known as redox reaction.

13.Oxidation: Oxidation is a chemical process in which a substance gains oxygen or loses hydrogen.

14.Reduction: Reduction is a chemical process in which a substance gains hydrogen or loses oxygen.