Lekhmir Singh Question Answer Chemical Equations and Reactions

Respiration is considered an exothermic process because energy is produced during this process.

A balanced chemical equation has an equal number of atoms of different elements in the reactants and products.

When quicklime is added to water, it forms slaked lime along with the evolution of heat. There will be a rise in temperature of the bucket.

Magnesium ribbon should be cleaned before burning in air to remove the protective layer of basic magnesium carbonate from its surface.

False.

Oxygen should be in molecular form, O2. The corrected and balanced equation is: 2Mg + O2 —–> 2MgO

The symbol (aq) represents an aqueous solution in a chemical equation.

Photosynthesis is considered an endothermic reaction because sunlight energy is absorbed by green plants during this process.

(a) Aqueous solution is indicated by the symbol ‘aq’.
(b) An exothermic reaction is indicated by writing “+Heat” or “+Heat energy” or “+Energy” on the products side of an equation.
(c) An endothermic reaction is indicated by writing “+Heat” or “+Heat energy” or “+Energy” on the reactants side of an equation.

(a) 2H2S + 3O2 —–> 2H2O + 2SO2
(b) P4 + 5O2 —–> 2P2O5
(c) CS2 + 3O2 —–> CO2 + 2SO2
(d) 2Al + Fe2O3 —–> Al2O3 + 2Fe
(e) BaCl2 + ZnSO4 —–> ZnCl2 + BaSO4

(a) Ca(OH)2 + CO2 —–> CaCO3 + H2O
(b) 2Al + 3CuCl2 —–> 2AlCl3 + 3Cu

(a) 2NaOH + H2SO4 —–> Na2SO4 + 2H2O
(b) Ca(OH)2 + CO2 —–> CaCO3 + H2O

Ca + 2H2O —–> Ca(OH)2 + H2
N2 + 3H2 —–> 2NH3

(a) Ca (s) + 2H2O (l) —–> Ca(OH)2 (aq) + H2 (g)
(b) 2SO2 (g) + O2 (g) —–> 2SO3 (g)

4Na + O2 —–> 2Na2O
2H2O2 —–> 2H2O + O2
Mg(OH)2 + 2HCl —–> MgCl2 + 2H2O
4Fe + 3O2 —–> 2Fe2O3
2Al(OH)3 —–> Al2O3 + 3H2O
2NH3 + 3CuO —–> 3Cu + N2 + 3H2O
Al2(SO4)3 + 6NaOH —–> 2Al(OH)3 + 3Na2SO4
2HNO3 + Ca(OH)2 —–> Ca(NO3)2 + 2H2O
2NaOH + H2SO4 —–> Na2SO4 + 2H2O
BaCl2 + H2SO4 —–> BaSO4 + 2HCl

(a) Conservation of mass
(b) Aqueous; (aq)

(a) Magnesium Ribbon is heated in the presence of air to form a white powder called magnesium oxide.
(b) When dilute sulphuric acid is poured over zinc granules:
– There will be a rise in temperature.
– Evolution of hydrogen gas.
(c) When potassium iodide solution is added to lead nitrate solution:
– A yellow precipitate is formed.
– There will be a change in color (from colorless to yellow).

(a) The method of representing a chemical reaction with the help of symbols and formulae of substances involved in it is called a chemical equation. Example: Zinc metal reacts with dilute sulphuric acid to form zinc sulphate and hydrogen gas. This equation is written as: Zn + H2SO4 —–> ZnSO4 + H2
(b) A balanced chemical equation has an equal number of atoms of different elements in the reactants and products. It has equal masses of various elements in the reactants and products.
Example: Zn + H2SO4 —–> ZnSO4 + H2
An unbalanced chemical equation has an unequal number of atoms of one or more elements in the reactants and products. It has unequal masses of various elements in the reactants and products.
Example: H2 + O2 —–> 2H2O
(c) 2NH3 —–> N2 + 3H2
C + CO2 —–> 2CO

H2 + CuO —–> Cu + H2O
Elements: H2 and Cu
Compounds: CuO and H2O
Reactants: H2 and CuO
Products: Cu and H2O
Metal: Cu
Non-metal: H2

(a) The various ways in which a chemical equation can be made more informative are:
(i) By indicating the physical states of the reactants and products. Example: Gaseous state is indicated by the symbol (g).
Zn (s) + H2SO4 (aq) —–> ZnSO4 (aq) + H2 (g)
(ii) By indicating the heat changes taking place in the reaction. For example: An exothermic reaction is indicated by writing “+Heat” or “+Heat energy” or “+Energy” on the products side of an equation.
C (s) + O2 (g) —–> CO2 (g) + Heat
(iii) By indicating the “conditions” under which the reaction takes place. Example: Delta stands for heat which is written over the arrow of the equation in the format.
(b) The balanced chemical equation is: Ca(OH)2 (aq) + CO2 (g) —–> CaCO3 (s) + H2O (l)