Read and the products with a suitable coefficient. equation by multiplying the reactants The chemical reaction which occurs by the absorption of heat from the surroundings is called an endothermic reaction. The chemical reaction in which heat is released to the surroundings is called exothermic reaction.
Test Your Concept
Tick $(\sqrt{ })$ the correct alternative (MCQs);
a. What is the type of change in which new substances with different properties are formed?
A) physical
B) chemical
C) reversible
D) both A) and B)
b. What are the substances that take part in a chemical reaction called?
A) products
B) solution
C) reactants
D) mixture
C. Which one of the following is the example of a chemical reaction?
A) melting of ice
B) rusting of iron
C) making a salt solution
D) magnetizing an iron nail
d. Which one of the following chemical reactions is an endothermic reaction?
A) $C + O _2 \longrightarrow CO _2$
B) $N _2+ O _2 \rightarrow 2 NO$
C) $Zn +2 HCl \longrightarrow ZnCl _2+ H _2$
D) $CaO + H _2 O \longrightarrow Ca ( OH )_2$
- Short answer type questions:
Answer (1)
Chemical changes form new substances, so the answer to question a is B) chemical.
Reactants are substances that take part in a chemical reaction, so the answer to question b is C) reactants.
Rusting of iron is a chemical reaction, so the answer to question c is B) rusting of iron.
N 2 + O 2 → 2 NO is an endothermic reaction, so the answer to question d is B) N 2 + O 2 → 2 NO .
Explanation
Analyzing the Questions We will analyze each multiple-choice question and select the correct answer based on the definitions of chemical reactions, endothermic reactions, and exothermic reactions.
Answering Question A a. The question asks about the type of change in which new substances with different properties are formed. This is the definition of a chemical change. Therefore, the correct answer is B) chemical.
Answering Question B b. The question asks about the substances that take part in a chemical reaction. These substances are called reactants. Therefore, the correct answer is C) reactants.
Answering Question C c. The question asks for an example of a chemical reaction. Among the options, rusting of iron is a chemical reaction because it involves the formation of a new substance (iron oxide) with different properties than iron. Melting of ice and making a salt solution are physical changes, and magnetizing an iron nail is a physical process. Therefore, the correct answer is B) rusting of iron.
Answering Question D d. The question asks for an example of an endothermic reaction. An endothermic reaction absorbs heat. Among the options, N 2 + O 2 → 2 NO is an endothermic reaction. The other reactions are exothermic reactions because they release heat. Therefore, the correct answer is B) N 2 + O 2 \tothe 2 NO .
Final Answer The answers to the multiple-choice questions are: a. B) chemical b. C) reactants c. B) rusting of iron d. B) N 2 + O 2 → 2 NO
Examples
Understanding chemical reactions is crucial in many real-world applications. For instance, in cooking, chemical reactions occur when we bake a cake, causing the ingredients to transform into a new substance with different properties. Similarly, in the development of new drugs, chemists rely on chemical reactions to synthesize molecules that can treat diseases. The principles of endothermic and exothermic reactions are also important in designing efficient energy systems, such as solar panels that absorb heat (endothermic) or combustion engines that release heat (exothermic).
