UPSC Prelims 2001 · General Studies

Question 116: Science and Technology

Assertion (A): A chemical reaction becomes faster at higher temperatures. Reason (R): At higher temperatures, molecular motion becomes more rapid. Which of the following is correct?

aBoth A and R are individually true and R is the correct explanation of A

bBoth A and R are individually true but R is NOT a correct explanation of A

cA is true but R is false

dA is false but R is true

AnswerThe answer is (a).

A is true: reactions usually go faster when the temperature rises. R is true and explains it: at higher temperatures the molecules move faster, collide more often and, more importantly, a larger fraction of collisions have enough energy to cross the activation energy barrier. Remember the rule of thumb that the rate roughly doubles for each 10 degree C rise.

A. Reaction rates rise with temperature.
R. Faster molecular motion gives more energetic collisions.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.

Which options go is worked out from UPSC’s key and the options, not by a model.

Why each option is right or wrong

(a) Right: both are true and R explains A.
(b) R is the explanation, not a side fact.
(c) R is true.
(d) A is true.

Explanation: written by UPSC Grade, not by UPSC.

Practise this paper timedNext question

Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.