Consider each of the following reactions and decide whether the standard entropy

Question

Consider each of the following reactions and decide whether the standard entropy change for the reaction will be large & positive; or small; or large & negative. 1. large&negative 2. large&positive 3.small

a) H2(g) + Cl2(g) = 2 HCl(g)

b) 2 Na(l) + H2(g) = 2 NaH(s)

c) 2 H2O(l) = 2 H2(g) + O2(g)

d) C(s) + H2O(g) = CO(g) + H2(g)

e) Cu(s) + 2 H2SO4(aq) = CuSO4(aq) + 2 H2O(l) + SO2(g)

f) BaSO4(s) + 2 H2O(g) = BaSO4.2H2O(s)

2. Identify the true statement(s) regarding the entropy of chemical substances.

All pure substances have a positive entropy at room temperature.

The dissolution of an ionic salt in water usually leads to an increase in entropy of the system (salt + water).

So(one mole O3(g)) > So(one mole O2(g)) at 25oC.

The entropy of ice at 0oC is lower than that of water at 0oC.

When a metallic crystal is heated, its entropy increases due to increasing atomic vibrations.

a) H2(g) + Cl2(g) = 2 HCl(g)

Explanation / Answer

The sign of S will be positive if there is an increase in temperature, an increase in the volume in which the molecules move, or an increase in the number of gas particles in the reaction. The question states that the temperature is constant. Thus, we need to evaluate each equation with the other two factors in mind.

H2(g) + Cl2(g) = 2 HCl(g)

Large and negative

Why- volume of reactant that is H2 and Cl2 is more compare to HCl.

2 Na(l) + H2(g) = 2 NaH(s)

Large and negative

You are converting gas and liquid to solid. Decrease in volume.

2 H2O(l) = 2 H2(g) + O2(g)

Large and positive.

Water is convert to H2 and O2, both are gases, so increase in volume.

C(s) + H2O(g) = CO(g) + H2(g)

Large and positive.

Cu(s) + 2 H2SO4(aq) = CuSO4(aq) + 2 H2O(l) + SO2(g)

Large and positive.

BaSO4(s) + 2 H2O(g) = BaSO4.2H2O(s)

Large and negative

You are converting gas and solid to liquid. Decrease in volume.

2. Identify the true statement(s) regarding the entropy of chemical substances.

All pure substances have a positive entropy at room temperature.

True

The dissolution of an ionic salt in water usually leads to an increase in entropy of the system (salt + water).

True

So(one mole O3(g)) > So(one mole O2(g)) at 25oC

True

The entropy of ice at 0oC is lower than that of water at 0oC.

True

When a metallic crystal is heated, its entropy increases due to increasing atomic vibrations.

True

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