Chemistry
(a) What is a chemical reaction?
(b) State the conditions necessary for a chemical change or reaction.
Chemical Reaction
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Answer
(a) A chemical reaction is a process of breaking chemical bonds of the reacting substances (reactants) and making new bonds to form new substances (products).
(b) Conditions necessary for a chemical change or reaction are :
Mixing (close contact) — Some chemical reactions take place when two substances are mixed in their solid state.
Pb(NO3)2 (s) + 2KI (s) ⟶ 2KNO3 + PbI2 (s)Solution — In some cases, a chemical reaction occurs when substances are mixed either in molten or aqueous state.
AgNO3 + NaCl ⟶ AgCl ↓ + NaNO3Heat — Some chemical reactions occur only on heating.
CuCO3 (s) CuO (s) + CO2 ↑ (g)Light — Some chemical reactions take place by the action of light. They are called photochemical reaction.
2AgNO3 2Ag + 2NO2 + O2 ↑Electricity — Some reactions are caused or accompanied by the passage of an electric current. They are called electrochemical reaction.
2NaCl 2Na + Cl2 ↑Pressure — Some chemical reaction take place only when the involved substances are subjected to high pressure.
N2 + 3H2 2NH3 ↑Catalyst — Some chemical reactions need a catalyst to accelerate or decelerate the rate at which they occur.
2H2O2 2H2O + O2 ↑
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Related Questions
Define the following terms:
(a) Chemical change
(b) Chemical bond
(c) Effervescence
(d) Precipitate
Give an example of a reaction where the following are involved:
(a) Heat
(b) Light
(c) Electricity
(d) Close contact
(e) Solution
(f) Pressure
(g) Catalyst
Define :
(a) Photochemical reaction
(b) Electrochemical reaction.
Give one example in each case.
Give an example of each of the following chemical changes.
(a) A photochemical reaction involving 1. silver salt 2. water
(b) A reaction involving 1. blue solution 2. formation of a dirty green precipitate
(c) Two gases combine to form a white solid.
(d) Two solids combine to form a liquid.
(e) A reaction where color change is noticed.