Chemistry
Assertion (A): When energy is absorbed during a chemical reaction, it is said to be an exothermic reaction.
Reason (R): A rise in temperature takes place during an exothermic reaction.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
A is false but R is true.
Explanation — Endothermic reactions absorb heat from the surroundings, while exothermic reactions release heat to the surroundings. Hence, if energy is absorbed, the reaction is endothermic, so Assertion (A) is false. In an exothermic reaction, heat released causes a rise in temperature, so Reason (R) is true.
Related Questions
Assertion (A): The reaction of an acid with a base to produce salt and water is called a neutralisation reaction.
Reason (R): Neutralisation reaction is a double displacement reaction.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): When a copper coil is dipped in an aqueous solution of silver nitrate, the colour of the solution slowly changes from colourless to blue.
Reason (R): Silver metal is more reactive than copper.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Fill in the blanks:
(a) A reaction in which two or more substances combine to form a single substance is called a …………… reaction.
(b) A …………… is a substance which changes the rate of a chemical reaction without undergoing a chemical change itself.
(c) The formation of gas bubbles in a liquid during a reaction is called …………… .
(d) The reaction between an acid and a base is called …………… .
(e) Soluble bases are called …………… .
(f) The chemical change involving iron and hydrochloric acid illustrates a …………… reaction.
(g) In the type of reaction called …………… two compounds exchange their positive an negative radicals respectively.
(h) A catalyst either …………… or …………… the rate of a chemical change but itself remains …………… at the end of the reaction.
(i) The chemical reaction between hydrogen and chlorine is a …………… reaction.
(j) When a piece of copper is added to silver nitrate solution, it turns …………… in colour.
Write true or false for the following and correct the false statements.
(a) When iron nails are put into a solution of copper sulphate, the solution becomes colourless after sometime.
(b) Burning of fuel in air produces a large amount of energy in the form of heat and light.
(c) Exchange of radicals takes place when calcium oxide reacts with water.
(d) A neutral oxide does not change the colour of an indicator.
(e) A white solid is produced when lead nitrate is heated.