Very short answer type questions (1-10):
1) Why is respiration considered an exothermic process?
Ans) Respiration is considered as an exothermic process because energy is released during respiration.
C6H12O6 + 6O2 —–> 6CO2 + 6H2O + energy
2) On what basis is a chemical equation balanced?
Answer: A chemical equation is balanced on the basis of Law of conservation of mass. The law states that matter can neither be created nor destroyed, i.e., the total mass of reactants is equal to the mass of the products.
3) What happens chemically when quicklime is added to water filled in a bucket?
Answer: When Calcium oxide i.e. quick lime is added to water filled in a bucket, it reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat
CaO + H2O —–> Ca(OH)2
4) Why should magnesium ribbon be cleaned before burning in air?
Answer: Magnesium ribbon is a reactive metal but its reactivity is partly inhibited because it reacts with oxygen in the air to form a layer of magnesium oxide on the magnesium ribbon. Since magnesium oxide is a thermal (heat) insulator, the layer of magnesium oxide should be cleaned by rubbing with a sand paper so that we can carry out the reaction using pure magnesium.
5) State whether the following statements is true or false:
A chemical equation can be balanced easily by altering the formula of a reactant or product.
Answer: False.
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6) What is wrong with the following chemical equation? Correct and balance it.
Mg + O —–> MgO
Ans) As Oxygen is an elementary gas, it should be written in its molecular form O2
2Mg + O2 —–> 2MgO
7) What does the symbol (aq) represent in a chemical equation?
Answer: The symbol (aq) represents aqueous. An aqueous solution is a solution in which the solvent is water.
8) Why is photosynthesis called an endothermic reaction?
Answer: Endothermic reactions are those which take place by absorbing heat. During photosynthesis, plants absorb energy from sunlight to turn carbon dioxide and water into oxygen and glucose. As the process of photosynthesis takes place by absorbing heat, it is considered to be an endothermic reaction.
6CO2 + 6H2O + heat —–> C6H12O6 + 6O2
9) How will you indicate the following effects in a chemical equation?
(a) A solution is made in water.
(b) Exothermic reaction.
(c) Endothermic reaction
Answer: The following effects are observed in a chemical equation when-
a) A solution is made in water- By using the subscript(aq) after the molecule.
(b) Exothermic reaction- An exothermic reaction is usually indicated by writing “+ heat” or “+Heat energy” or just “+ energy” on the products side (RHS) of a chemical equation
E.g., C (s) + O2(g) —–> CO2(g) + Heat
(c) Endothermic reaction- An endothermic reaction is usually indicated by writing “+ heat” or just “+ energy” on the reactants side (LHS) of a chemical equation
Eg., CaCO3(s) + heat —–> CaO(s) + CO2(g)
10) Translate the following statements into chemical equations and then balance the equations:
a) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
b) Phosphorous burns in oxide to give phosphorous pentoxide.
c) Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide
d) Aluminium metal replaces iron from ferric oxide, Fe2O3, giving aluminium oxide and iron.
e) Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate.
Answer: a) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
2H2S + 3O2 —–> 2H2O + 2SO2
b) Phosphorous burns in oxide to give phosphorous pentoxide
P4+ 5O2 —–> 2P2O5
c) Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide
Ans) CS2 + 3O2 —–> CO2 + 2SO2
d) Aluminium metal replaces iron from ferric oxide, Fe2O3, giving aluminium oxide and iron
2Al + Fe2O 3 —–> Al2O3 +2Fe
e) Barium chloride reacts with zinc sulphate to give zinc chloride and barium sulphate.
BaCl2 + ZnSO4 —–> ZnCl2 + BaSO4
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