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  1. The combination or displacement that occurs in the molecules of matter during a chemical change called a chemical reaction. Any two examples are:

    1. 2H2 + 02 -------> 2H20
    2. H2SO4 + Zn ---------> ZnSO4 + H2

  2. A chemical reaction expressed by writing the full names of reactants and products is called a word equation. For example:

    Hydrogen + oxygen -----------> Water

  3. A chemical equation is an equation that represents the chemical reaction with the symbols and molecular formulae of the reactants and products.

    For example:    2H2 + 02 --------> 2H2O

  4. The elements or compounds that take part in a chemical reaction are reactants and the elements or compounds that are formed as a result of a chemical reaction are called products.

    for example

    H2SO4 + Zn ----------> ZnSO4 + H2

    Reactants                    Products

  5. A chemical eqn. which contains an equal number of atoms of each element in both reactant and product side is called balanced chemical eqn.

    Example: 2H2 + O2 --------> 2H2O

  6. Any three pieces of info that can be obtained from a balanced chemical eqn are:

    1. The type of chemical reaction.
    2. The name and symbol of reactants and products.
    3. The total number of atoms of reactants and products.

  7. Four factors that bring about a chemical change are:

    > Heat                               > Catalyst
    > Light                               Solution
    > Pressure                        > Electricity

  8. A catalyst is a chemical substance that increases or decreases the rate of a chemical reaction without taking part in a chemical reaction.

    The +ve catalyst is the chemical substance that increases the rate of a chemical reaction. For example MnO2The catalyst is the chemical substance that decreases the rate of a chemical reaction. For example glycerine.

  9. A chemical reaction in which two or more reactants are combined together to give a single product is called a combination reaction. Examples are:

    C + O2 --------> CO2
    C + 2H2 ---------> CH4

  10. A chemical reaction in which a single reactant is broken down into two or more products called a decomposition reaction. For example:

    CaCO3 -------> CaO + CO2
    CuCO3 -------> CuO + CO2

  11. A chemical reaction in which an atom of a compound is displaced by another element is called a displacement reaction. Its types are:

    1. Single displacement rxn.
    2. Double displacement rxn.

  12. A chemical reaction in which aid and base react together to gee salt and water is called an acid-base reaction.

    It is called a neutralization reaction because the acidic and basic nature of compounds is neutralized during the reaction.

  13. The atomic weight of an element expressed in grams is called gram atomic weight.

    The molecular weight of a substance expressed in grams is called molecular weight.

  14. The amount of a substance that contains 6.023 X 1023 atoms or ions is called moles.

    Avogadro's number is the number of particles in one mole of a substance.

    NA6.023 X 1023

  15. The burning of magnesium in the air conducts that reaction where magnesium and oxygen combine to form magnesium oxide. As two elements combine each other, it is called a combination reaction.

    2Mg + O2 ------> 2MgO

  16. We know, a chemical reaction in which an acid and base react together to give salt and water is called an acid-base reaction. Here acidic and basic nature et compounds are neutralized. So, it called a neutralization reaction.

  17. We know, water breaks down into hydrogen and oxygen during its electrolysis. As two elements decompose themselves in this chemical reaction, it is called a decomposition reaction.

    2H20 --------> 2H2 + O2

  18. The positive change in the concentration of a reactant or a product per unit time is called the rate of a chemical reaction. Any four factors that affect the rate of a chemical reaction are:

    1. The concentration of reactants
    2. Temperature
    3. Physical nature of reactants
    4. Chemical nature of reactants

  19. An increase in temperature increases the rate e chemical reaction whereas a decrease in temperature decreases the rate of a chemical reaction.

    Positive catalyst increases and negative catalyst decreases the rate of a chemical reaction.

  20. When the concentration of Sodium thiosulphate was increased the rate of reaction increased and the time taken to reach equilibrium decreased, so therefore the rate of reaction is directly proportional to the concentration. So rate of reaction increases.


  21. a. Reactants and products.

    ReactantsProducts
    The chemicals that undergo chemical changes are reactants.The chemicals that are formed as a result of the reaction are products.
    These are the chemicals before the reaction between them occurs.These are the chemicals after the reaction between them occurs.

    b. Word equation and formulae equation.

    WordFormulae
    It is the representation of chemical equations by words.It is the representation of chemical equations by symbols.
    It is less informative.It is more informative.
    It is longer and non-convenient.It is shorter and convenient.

    c. Combination reaction and decomposition reaction.

    CombinationDecomposition
    In this reaction, different reactants are combined to form a single product.In this reaction, a single reactant is decomposed to form multiple products.
    It occurs either in the presence or absence of heat.It occurs in the presence of heat only.

    d. Positive catalyst and negative catalyst.

    PositiveNegative
    It increases the rate of a chemical reaction.It decreases the rate of a chemical reaction.
    It is used to accelerate the reaction.It is used to slow down the reaction.
    Mn02 is an example.Glycerine is an example.