Question

In an ideal rubber, the primary factor responsible for elasticity up to small strains is

• A. Change in both enthalpy and entropy
• B. Change in enthalpy, but no change in the entropy
• C. No change in enthalpy, but change in the entropy
• D. Neither a change in enthalpy, nor a change in the entropy

Hint:

Ideal rubber behaves as an entropic spring: elasticity primarily comes from entropy change, not energy change.

Answer 1

The Correct Option is C

In an ideal rubber, elasticity does not arise from internal energy (enthalpy) changes. Instead, the elasticity comes from the entropy-driven restoring force of the long-chain polymer molecules. When rubber is stretched, the polymer chains become more ordered, reducing entropy. When released, the system returns to a higher entropy state, producing an elastic restoring force. Thus, enthalpy remains nearly constant, while entropy changes significantly.