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Thermochemistry

This review covers concepts related to spontaneous chemical reactions, including the conditions that determine spontaneity based on ΔH and ΔS values, the impact of ΔG and ΔT on reaction spontaneity, and factors that can change ΔG. It also discusses the relationship between ΔH, ΔS, and the evaporation process, as well as predictions about products and reactions.

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Thermochemistry

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  1. Thermochemistry Review

  2. Which of the following describes a system that CANNOT be spontaneous? • ΔH is positive and ΔS is negative • ΔH is positive and ΔS is positive • ΔH is negative and ΔS is negative • ΔH is negative and ΔS is positive 10

  3. Which of the following must be negative for a reaction to be spontaneous? • Δ G • ΔS • Δ H • ΔT 10

  4. If ΔH is ____ and ΔS is ___ and reaction will never be spontaneous. • Positive, positive • Positive, negative • Negative, negative • Negative, positive 10

  5. Which of the following explains why, when KCl is dissolved, water condenses on the side of the beaker? • ΔH is positive and ΔS is negative • ΔH is positive and ΔS is positive • ΔH is negative and ΔS is negative • ΔH is negative and ΔS is positive 10

  6. Which of these is least probable for a combustion reaction? • ΔG is a large negative number • ΔS is a large negative number • ΔH is a large negative number • Q is a small number 10

  7. The rate of a reaction will be large if • ΔG is a large negative number • ΔS is a large negative number • ΔH is a large negative number • None of the above 10

  8. Which of the following can change the value of ΔG for a chemical reaction? • Changes in total pressure • Changes in the pressures of the reactants • Changes in the concentrations of the reactants • Changes in the temperature • The presence of a catalyst 10

  9. At what tempterature is Keq = 1.00 if ΔS = 22.6 J/K and ΔH = 15.3 kJ for a chemical reaction? • 404 o C • 677 o C • 0.67oC • 1477oC • 1204oC 10

  10. The reaction below is expected to have2C6H6(l) + 15O2(g) 12CO2(g) + 6H20(l) • A positive ΔH and a negative ΔS • A negative ΔH and a negative ΔS • A positive ΔH and a positive ΔS • A negative ΔH and a positive ΔS • Not possible to determine 10

  11. The evaporation of any liquid is expected to have • A positive ΔH and a negative ΔS • A negative ΔH and a negative ΔS • A positive ΔH and a positive ΔS • A negative ΔH and a positive ΔS • These predictions cannot be made 10

  12. Which of the following is most likely to be true? • No products are formed in a nonspontaneous reaction. • A positive ΔG indicates a spontaneous reaction. • A positive ΔS always means that the reaction is spontaneous • A spontaneous reaction always goes to completion • Combustion of organic compounds has a negative ΔH 10

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