Chemical reactions and equations

chemical reactions and equations class 10

1. Chemical Reactions And Equations

2. CHEMICAL REACTIONS Chemical Reactions are associated with chemical change. Rearrangement of atoms of a substance takes place. Whenever a chemical change occurs chemical reaction is said to take place. Chemical reactions are usually irreversible and a new product is formed.

3. Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: Change in color Evolution of a gas Change in temperature Change in state Formation of precipitate

4. Word Equations A WORD EQUATION describes chemical change using the names of the reactants and products . The word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactant Product CH 4 + 2 O 2 CO 2 + 2 H 2 O

5. Chemical Equation The simplest form of description of a chemical reaction in a shorter form is by writing it in the form of an equation. E.g.- Mg + O 2 MgO The reactants are written on the left side and product is written on the right side. An arrow is placed between them to show the direction of reaction.

6. Characteristics of Chemical Equations The equation must represent known facts. The equation must contain the correct formulas for the reactants and products. The law of conservation of mass must be satisfied.

7. Showing phases in Chemical Equations H 2 O(s) H 2 O(l) H 2 O(g) Solid Phase – the substance is relatively rigid and has a definite volume and shape. NaCl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H 2 O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl 2 (g)

8. Balanced Chemical Equations According to the law of conservation of mass, total mass must be equal on the both sides of the equation. This type of equation is known as a balanced chemical reaction. E.g.- 2 Mg + O 2 2MgO Here both sides have two atoms of Magnesium and two atoms of Oxygen.

9. Unbalanced and Balanced Equations H Cl Cl Cl H H H H Cl Cl Cl H Cl H H 2 + Cl 2  HCl H 2 + Cl 2  2 HCl (unbalanced) (balanced) reactants products reactants products reactants products H Cl reactants products H Cl 2 1 2 1 2 2 2 2

10. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

11. Types of Chemical Reactions Combination reaction 2. Decomposition reaction 3. Single-displacement reaction 4. Double-displacement reaction A + B  AB AB  A + B A + BC  AC + B AB + CD  AD + CB 5. Redox reaction

12. These type of reactions occur when two reactants combine to form one or more products. E.g. – CaO + H 2 O Ca(OH) 2 C + O 2 CO 2 They are generally exothermic reactions which involve evolution of heat during reaction. Combination Reactions

13. Combination Reaction General form: A + B  AB element or element or compound compound compound Cl Na Cl 2 Na + Cl 2  2 NaCl  Na Na NaCl NaCl +

14. Decomposition Reaction The types of reaction in which a single reactant breaks down to give simpler products are called decomposition reaction. E.g.- When a decomposition reaction is carried out by heating, it is known as thermal decomposition . 2 H 2 O 2 H 2 + O 2

15. H H Decomposition Reaction H H H H O Decomposition reaction 2 H 2 O 2 H 2 O 2 General form: AB A B + + + compound two or more elements or compounds O O O H H

16. Decomposition Reactions H 2 O H 2 + O 2 electricity H 2 O 2 H 2 O + O 2 NI 3 N 2 + I 2 2 2 Hydrogen Peroxide Electrolysis of water 2 2 Nitrogen triiodide AB A + B General Form 2 3

17. Displacement Reactions The reaction in which a more reactive element displaces a less reactive element from its solution is known as displacement reaction. They are of two types:- Single Displacement Reaction Double Displacement Reaction

18. Single and Double Displacement Reactions Double-displacement reaction:- CaCO 3 + 2 HCl  CaCl 2 + H 2 CO 3 General form: AB + CD  AD + CB Single-displacement reaction:- Mg + CuSO 4  MgSO 4 + Cu General form: A + BC  AC + B

19. PbI 2 K 1+ Pb 2+ lead (II) chloride + potassium iodide Cl 2 I Pb 2+ Pb K 1+ K Cl 1- I 1- Cl 1- I 1- KCl potassium chloride lead (II) iodide + (aq) (ppt) + + Single Displacement Reaction A reaction that yields an insoluble product, a precipitate, when two solutions are mixed are a subclass of exchange reactions that occur between ionic compounds when one of the products is insoluble Used to isolate metals that have been extracted from their ores.

20. Double Displacement Reaction K 2 CO 3 ( aq ) Potassium carbonate BaCl 2 ( aq ) Barium chloride 2 KCl ( aq ) Potassium chloride BaCO 3 ( s ) Barium carbonate + +

21. Redox Reactions If a substance gains oxygen during a reaction, it is said to be oxidised . If a substance loses oxygen during a reaction, it is said to be reduced. Reactions in which this type of change occurs is known as Oxidation and Reduction reactions or Redox reactions. E.g. – CuO + H 2 Cu + H 2 O

22. ABHINAV RATURI Xth-D ROLL No. 19 Thanks For Watching.