Case Based Questions (MCQ)

Class 10
Chapter 1 Class 10 - Chemical Reactions and Equations

## Chemistry in Automobiles: For an internal combustion engine to move a vehicle down the road, it must convert the energy stored in the fuel into mechanical energy to drive the wheels. In your car, the distributor and battery provide this starting energy by creating an electrical "spark", which helps in combustion of fuels like gasoline. Below is the reaction depicting complete combustion of gasoline in full supply of air:

### Product ‘X’           Product ‘Y’

1. CO 2           H 2 O 2
2. H 2 O          CO
3. CH 3 OH    H 2 O
4. CO 2          H 2 O

In a Combustion reaction,

Fuel burns in oxygen to form Carbon Dioxide and Water

2C 8 H 18 (l) + 25O 2 (g) → 16CO 2 + 9H 2 O

So, the correct answer is (d)

### d) Combination & Endothermic reaction

Here

• Decomposition Reaction:  The reaction in which complex compounds are broken down into simpler ones i.e. AB → A + B
• Oxidation Reaction: The reaction in which an oxygen atom is gained i.e. A + O 2 → AO 2
• Combination Reaction: When two or more substances combine to form a single product i.e. A + B → AB

And,

• Endothermic Reaction: Endo means in and thermic means heat. In these reactions, heat is absorbed.
• Exothermic Reaction: Exo means out and thermic means heat. In these reactions, heat is released.

Since in Combustion

• Energy is released
• Oxygen is gained

Thus, it is an oxidation and exothermic reaction

So, the correct answer is (c)

### (d) (ii) & (i)

In a Combustion reaction, heat is released (evolved)

Let’s check all the options:

1. In photosynthesis , the plants make food by absorbing the energy of the sun.
So, this is not similar to Combustion

2. The breakdown of food to release energy is known as respiration . Hence, energy is released.
So, this is similar to Combustion

3. Decomposition of vegetable matter involves release of energy.
So, this is similar to Combustion

4. In order to carry out the decomposition of ferrous sulphate, we need to supply heat.
So, this is not similar to Combustion

So, the correct answer is (a)

### d) Limited supply of air leads to complete combustion of fuel.

In the presence of limited supply of air, there isn’t enough oxygen to carry out complete combustion of fuels. Therefore, incomplete combustion takes place and a black sooty flame is observed

### d) Only hydrocarbons can take part in combustion

In nitrogen gas i.e. N 2 , there are three bonds between the nitrogen atoms.

Therefore, it is v ery difficult to break these.

Since a chemical reaction occurs by breaking and making of chemical bonds, nitrogen is relatively a very inert gas and therefore, doesn’t undergo combustion.

So, the correct answer is (b)

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