CHEMICAL REACTIONS AND
EQUATIONS
1.
A
When do we say that a chemical reaction has taken place?
Whenever a chemical change occurs we say that a chemical reaction
has taken place.
2.
A.
What is the colour of the flame on heating magnesium?
White dazzling flame.
3.
A.
What powder is formed on heating magnesium?
Magnesium oxide.
4.
What are the observations which determine whether a chemical reaction
has taken place or not?
(a) Change in state
(b) Change in colour
(c) Evolution of gas
(d) Change in temperature
A.
5.
A.
What are reactants?
The substances that undergo chemical change are the reactants.
6.
A.
Where are reactants written in a chemical equation?
On the left hand side.
7.
A.
Where are products written in a chemical equation?
On the right hand side.
8.
A.
Which points towards the products and shows the direction of the reaction?
The arrowhead points towards the products and shows the direction of the
Reaction.
9.
A.
Which chemical equations are called skeletal chemical equations?
The chemical equations in which mass of products is not equal to mass of
reactants are called skeletal chemical equations.
10. What is law of Conservation of mass?
A. Mass can neither be created nor be destroyed.
11. When is the equation said to be a balanced equation?
A. When the number of atoms of elements of both reactants and products are
equal.
12. What is hit and trail method?
A. The method of equating number of atoms of elements on both sides is called hit
and trail method.
13. Why is this called hit and trail method?
A. Since we make trails to balance the equation by using the smallest whole
number coefficient.
14. How can we make a chemical equation more informative?
A. By mentioning physical states of the reactants and products along with their
chemical formula.
15. What does chemical reactions involve?
A. Chemical reactions involve the breaking and making of bonds between atoms to
produce new substances.
16. What is combination reaction?
A. The reaction in which a single product is formed from two or more reactants is
known as a combination reaction.
17. What is the chemical formula of marble?
A. CaCO3 (Calcium carbonate).
18. Give some examples of combination reactions.
A. (a) Burning of coal
C(s) + O2
CO2
(b) Formation of water from H2 (g) and O2 (g)
2H2(g) + O2 (g)
2H2O (l)
19. What are exothermic chemical reactions? Give some examples.
A. Reactions in which heat is released along with the formation of products are
called exothermic reactions.
Ex:- (a) Respiration.
(b) Burning of natural gas. [CH4 (g) + 2O2 (g)
CO2 (g) + 2H2O (g)]
(c) Decomposition of vegetable matter into compost.
20. What happens during digestion?
A. During digestion, food is broken down into simpler substances.
21. What is respiration?
A. The process in which carbohydrates are broken down to glucose. This glucose
combines with oxygen in cells of our body and provides energy. This is called
respiration. [C6H12O6 (a) + 6O2 (aq)
6CO2 (aq) + 6H2O (l) + energy]
22. What is decomposition reaction?
A. The reactions in which a single reactant breaks down to give simpler substances
is called decomposition reaction.
Ex: - (a) 2FeSO4 (s)
Fe2O3 (s) + SO2 (g) + SO3 (g)
(b) CaCO3 (s)
CaO (s) + CO2 (g)
(c) 2Pb(NO)3 (s)
2PbO (s) + 4NO2 (g) + O2 (g)
23. What is the colour of nitrogen dioxide?
A. Brown
24. What happens to silver chloride and silver bromide when exposed to sunlight?
A.
Silver chloride and silver bromide decomposes to silver and chlorine and silver
and bromine respectively.
25. Which reactions are used in black and white photography?
A. (a)2AgCl (s)
2Ag (s) + Cl2 (g)
(b)2AgBr (s)
2Ag(s) + Br2 (g)
26. What are endothermic reactions?
A. Reactions in which energy is absorbed are known as endothermic reactions.
27. Which forms of energy are required for decomposition reactions?
A. Heat, light or electricity.
28. What are displacement reactions?
A. The reactions in which one element displaces another element from its
compound
are called displacement reactions.
Ex: - (a) Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(b) Zn (s) + CuSO4 (aq) →
ZnSO4 (aq) + Cu (s) →
(c) Pb (s) + CuCl2
→
PbCl2 (aq) + Cu (s)
30. What is precipitate?
A. The insoluble substance produced in precipitation reactions is called precipitate.
31. What are double displacement reactions?
A. The reactions in which there is an exchange of ions between the reactants are
called double displacement reactions.
Ex: - Na2SO4 (aq) + BaCl2 (aq)
BaSO4 (s) + 2NaCl (aq)
32. When do we say that a substance is oxidized?
A. If a substance gains oxygen or loses hydrogen during a reaction, it is said to be
oxidised.
33. When do we say thata substance is reduced?
A. If a substance loses oxygen or gains hydrogen during a reaction, it is said to be
reduced.
34. What are oxidation-reduction or redox reactions?
A. When one reactant get oxidised while the other gets reduced during a reaction,
Such reactions are called oxidation-reduction or redox reactions.
Ex: - CuO + H2
heat
Cu + H2O
ZnO + C
Zn + CO
MnO2 + 4HCl
MnCl2 +
2H2O + Cl2
35. What is rusting of iron?
A. The process in which shiny iron articles are coated with a reddish brown powder
when left for some time is commonly known as rusting.
36. What is corrosion?
A. When a metal is attacked by substances around it such as moisture, acids, etc.,
it is said to corrode and this process is called corrosion.
37. What are antioxidants?
A. The substances, which prevent oxidation, are called antioxidants.
38. How can we prevent rancidity?
A. 1.By using antioxidants.
2.By keeping food in airtight containers.
3.By keeping food in inert gases like nitrogen.
39. How can keeping food in airtight containers prevent rancidity?
A. Keeping food in airtight containers slows down oxidation.
40. Which reactions produce insoluble salts?
A. Precipitation reactions.
41. When is a chemical equation said to be complete?
OR
What are the constituents of complete chemical equation?
A. A complete chemical equation represents the reactants, products and their
Physical states symbolically.