Chemical Reactions And Their Types
Class 8th Science (old) MHB Solution
- Name the different types of chemical reactions. Answer the following questions.…
- Explain the difference between a combination and dissociation reaction. Answer the…
- Explain with examples what is meant by oxidation. Answer the following questions.…
- Explain with examples what is meant by reduction. Answer the following questions.…
- What is a catalyst? Answer the following questions.
- On what factors does the speed of chemical reactions depend? Answer the following…
- Of which type is each of the following reactions? (a) CaO + H2O — Ca(OH)2 + Heat (b) C+ O2…
- Write the equations for each of the following reactions and name the reactants and…
- Match the following.
Exercises
Question 1.Answer the following questions.
Name the different types of chemical reactions.
Answer:
Different types of chemical reactions are:
•Combination Reaction
•Decomposition or Dissociation Reaction
•Displacement Reaction
1.Combination Reaction:
Two or more reactants unite to form a single product.
General Form: A + B -> AB
Eg: S + O2 ---------> SO2
2.Decompostion Reaction
A single reactant is decomposed or broken down into two or more
products.
General Form: AB -> A + B
Eg: CaCO3 ----------> CaO + CO2
3.Displacement Reaction
A reaction in which one constituent displaces another and separates is called displacement reaction.
General Form : A + BC -> B + AC
Eg: Zn + 2 HCl ----------> H2 + ZnCl2
Question 2.
Answer the following questions.
Explain the difference between a combination and dissociation reaction.
Answer:
A combination reaction (also known as a synthesis reaction) is a reaction where two or more elements or compounds (reactants) combine to form a single compound (product).
Such reactions may be represented by equations of the following form: X + Y → XY.
Here X and Y are the reactants and XY is the product.
Eg:
A dissociation reaction is a chemical reaction where a compound breaks apart into two or more parts.
The general formula for a dissociation reaction follows the form: AB → A + B.
Dissociation reactions are usually reversible chemical reactions.
Eg:
Question 3.
Answer the following questions.
Explain with examples what is meant by oxidation.
Answer:
In general, a reaction where oxygen is added or gained is called oxidation reaction. This definition is with respect to oxygen addition.
Eg:
While a reaction where hydrogen is removed is also called oxidation reaction. An oxidizing agent (substance or chemical used for removal of hydrogen) is required to remove the hydrogen.
Question 4.
Answer the following questions.
Explain with examples what is meant by reduction.
Answer:
A reaction where hydrogen is added or oxygen is removed is termed as reduction reaction. A reducing agent is used for this purpose.
Eg:
Question 5.
Answer the following questions.
What is a catalyst?
Answer:
Substances that can alter or change the rate of a reaction are called catalyst. In simple words certain substances are added during a reaction to improve the speed of formation of products or to decrease the formation of unwanted products ae catalysts.
Eg: Hydrogen peroxide will decompose into water and oxygen gas. Two molecules of hydrogen peroxide will produce two molecules of water and one molecule of oxygen. A catalyst of potassium permanganate can be used to speed up this process.
Question 6.
Answer the following questions.
On what factors does the speed of chemical reactions depend?
Answer:
There are several factors that affect the speed of a reaction:
Some of them are: (of a reaction)
•Nature of the reactants.
•Particle size of the reactants.
•Concentration of the reactants.
•Pressure of gaseous reactants.
•Temperature.
•Catalysts.
Question 7.
Of which type is each of the following reactions?
(a) CaO + H2O —> Ca(OH)2 + Heat
(b) C+ O2 —>CO2
(c) Cl2+ H2 --> 2HCl
(d) 2Mg + O2---> 2MgO
Answer:
(a) Exothermic reaction. Because on the product side heat is emitted. Exothermic reaction is one where heat is emitted.
(b) Combination reaction. Carbon and Oxygen combines together under certain condition to form carbon dioxide.
But this reaction can be a Combustion Reaction also. Because the burning of a compound with evolution of considerable amount of heat energy is called combustion. In this reaction C (carbon) is burnt in O2 (Oxygen) and release heat energy.
(c) Combination Reaction as well as Reduction reaction.
As Hydrogen is added, this is a reduction reaction. And two compounds combine to form one, so a combination reaction too.
(d) This is a Combination and Oxidation reaction. As two products are added, it’s a combination, while oxygen is one of the reactant which is added to the products, so it’s an oxidation reaction.
Question 8.
Write the equations for each of the following reactions and name the reactants and products of each.
(a) Coal was burnt in air.
(b) Magnesium wire was lit.
(c) Dilute hydrochloric acid was poured on to some zinc.
(d) Water was poured on calcium oxide.
Answer:
(a) C+ O2 —>CO2
Reactants: Carbon\Coal and Oxygen
Products: Carbon Di Oxide
(b) 2Mg + O2---> 2MgO
Reactants: Magnesium and Oxygen
Products: Magnesium Oxide (MgO)
(c) Zn + 2HCl → ZnCl2 +H2
Reactants: Zinc and Hydrochloric acid
Products: Zinc chloride and Hydrogen gas
(d) CaO + H2O → Ca(OH)2
Reactants: Calcium Oxide and Water
Products: Calcium Hydroxide
Question 9.
Match the following.
Answer:
Activities
Question 1.Observe what happens when lemon juice falls on a Shahbad tile.
Answer:
When lemon juice falls on shahbad tile which contains calcium carbonate the following chemical reaction occurs:
Calcium carbonate + lemon juice → Calcium Citrate +CO2 gas
Calcium Citrate formed on tile leaves a white mark on tile which can be cleaned with water.
Question 2.
Find out about the effects that perfumes have on jewelry / ornaments.
Answer:
Oils and chemicals in perfume can cause tarnish on silver or silver-plated jewelry, it can also damage other types of jewelry; porous stones and gems and costume jewelry. Tarnish can be removed from silver jewelry with a silver polishing cloth or ultrasonic jewelry cleaning machine.