Question

Which of the following processes/reactions have a negative entropy change? Which of the following processes/reactions have a negative entropy change?

a) Sublimation of dry ice into CO2 gas

b) Cs metal melting in your palm

c) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)

d) 2 CH4(g) → C2H2(g) + 3 H2(g)

Answer 1

  Entropy is the measure of disorder in a system.
Order in a system equates to low entropy, while disorder in a system equates to high entropy.
For example, for a given substance, the entropy of a gas is greater than the entropy of the liquid or of the solid. Why? The particles aren't moving around NEARLY as much in the solid or liquid as they are in the gas. They aren't as random. They are more rigid, and thus, have more order to them, and lower entropy.
Let's say that I take a bag of bouncy-balls and let them go...with them bouncing everywhere, and in a random order, this would be high (positive) entropy in the bouncy-ball system

a] Solid to liquid - Positive

b] Solid to liquid - Positive

c] No of gas molecules in the reactants side are more ... So entropy is negative

d] Entropy is positive

Answer is c) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)