We’re being asked to predict how the entropy of each substance is affected by the given process.
Recall that entropy is the degree of chaos or disorder of a system and that it depends on the following:
1. Phase: The gas phase has the highest entropy, followed by the liquid, and then the solid phase with the lowest entropy.
Gas > Liquid > Solid
2. Complexity: More elements in the compound leads to higher entropy.
Ex. NO3(g) [4 elements] has higher entropy than NO2(g) [3 elements].
3. Mass: The greater the mass, then the greater the entropy.
Ex. Xe(g) [greater mass] has higher entropy than He(g).
For a given process, entropy (ΔS) will either increase or decrease.
Remember that phase changes lead to a change in entropy:
Predict how the entropy of the substance is affected in the following processes:
a) Ar(l) → Ar(g)
b) Cu(s, 300 K) → Cu(s, 800 K)
c) H2O (g, 75 Torr, 300 K) → H2O(g, 150 Torr, 300 K)
Which of the following reactions have a positive ΔSrxn? Check all that apply.
a) A(s) + B(s) → C(g)
b) A(g) + B(g) → C(g)
c) 2A(g) + B(g) → 4C(g)
d) 2A(g) + B(g) → C(g)
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What scientific concept do you need to know in order to solve this problem?
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