Chemistry · Chemical thermodynamics · chapter 5 of 9

Class 11 Chemistry Chapter 5: Thermodynamics Assertion-reason questions with answers

2 assertion-reason questions on Thermodynamics, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): A mixture of hydrogen and oxygen can be kept at room temperature for years without any perceptible change, yet the formation of water from it is a spontaneous reaction. Reason (R): Spontaneity means the potential to proceed without external help; it says nothing about the rate.
Show answer

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true, and R is why A is not a contradiction: the reaction is spontaneous but extremely slow.

Question 2
Assertion (A): The heat measured when a substance is burnt in a bomb calorimeter is the change in internal energy, ΔU. Reason (R): The steel bomb is immersed in a water bath so that no heat is lost to the surroundings.
Show answer

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true. A holds because the sealed bomb keeps the volume constant (ΔV = 0, no work), so qV = ΔU; the water bath only collects the heat, so R does not explain A.

Take the free Class 11 Chemistry testSee the Class 11 flashcards

← Chapter 4: Chemical Bonding and Molecular StructureChapter 6: Equilibrium →