General Chemistry Answers

Calculate the reaction free energy of

H₂(g) + Cl₂(g)   2HCl(g)

when the concentrations are 0.026 mol L^-1 (H₂), 0.033 mol L^-1 (Cl₂), and 0.00184 mol L^-1 (HCl), and the temperature is 500K. For this reaction K_c = 85 at 500 K.

1. -5.3 kJ
2. -12.2 kJ
3. -22.2 kJ
4. -41.5 kJ

At high temperatures some non-spontaneous chemical reactions become spontaneous. Which of the following conditions must occur?

1. ΔS°> 0, Δ H°> 0
2. ΔS°> 0, Δ H°< 0
3. Δ S°< 0, ΔH°< 0
4. ΔS° < 0, ΔH°> 0

You are given pure samples of ammonia, NH₃(g), and nitrogen trifluoride, NF₃(g). What prediction would you make concerning their standard molar entropies at 298 K?

1. S°_ammonia > S°_{nitrogen trifluoride}
2. S°_ammonia< S°_{nitrogen trifluoride}
3. S°_{ammonia ≈}S°_{nitrogen trifluoride}
4. More information is needed to make reasonable predictions.

Predict the sign of ΔS°for the following reaction.

O₃(g) + NO(g) → O₂(g) + NO₂(g)

1. ΔS°≈0
2. ΔS°< 0
3. ΔS°> 0
4. More information is needed to make a reasonable prediction.

Which one of the following is an incorrect formation reaction?

1. H₂(g) + ½O₂(g) → H₂O(l)
2. H₂(g) + O₂(g) →H₂O₂(l)
3. Ca(s) + ½O₂(g) → CaO(s)
4. C(graphite) + 4H(g) →CH₄(g)
5. 2Fe(s) + 3/2O₂(g) → Fe₂O₃(s)

Nitric acid has been made for hundreds of years since its discovery about 1100. The reaction is: NaNO₃ + H₂SO₄ → HNO₃ + NaHSO₄ Calculate the Δ H° _rxn for the reaction. Δ H° _f [NaNO₃(s)] = -467kJ/mol; Δ  H° _f [H₂SO₄(l)] = -814 kJ/mol; 

Δ  H° _f [HNO₃(l)] = -174 kJ/mol; 

Δ  H° _f [NaHSO₄(s)] = -1126 kJ/mol;

1. -19 kJ
2. -2581 kJ
3. 19 kJ
4. 329 kJ

A piece of copper metal is initially at 100.0° C. It is dropped into a coffee cup calorimeter containing 50.0 g of water at a temperature of 20.0° C. After stirring, the final temperature of both copper and water is 25.0° C. Assuming no heat losses, and that the specific heat (capacity) of water is 4.18 J/(g·K), what is the heat capacity (not spectific heat capacity) of the copper in J/K?

1. 2.79
2. 3.33
3. 13.9
4. 209
5. None of the above

Galena is the ore from which elemental lead is extracted. In the first step of the extraction process, galena is heated in air to form lead(II) oxide.

2PbS(s) + 3O₂(g) → 2PbO(s) + 2SO₂(g) Δ H = -827.4 kJ

What mass of galena is converted to lead oxide if 975 kJ of heat are liberated?

1. 203 g
2. 282 g
3. 406 g
4. 564 g

The enthalpy (H) of liquid water is greater than that of the same quantity of ice at the same temperature.

1.  True
2.  False

A system delivers 225 J of heat to the surroundings while delivering 645 J of work. Calculate the change in the internal energy, Δ E, of the system

1. -420 J
2. 420 J
3. -870 J
4. 870 J