C2 Q1 Review

The reactions for the combustion of diamond and graphite are shown at the side. Which of the following values is closest to the ΔH_rxn for the conversion of C_(graphite) to C_(diamond)? 

• −789 kJ 

• −1.9 kJ

• 1.9 kJ 

• 394.45 kJ

• 798 kJ

A quantity that is zero for a pure element in its standard state refers to

• Enthalpy of formation 

• Entropy

• Energy of crystallization

• Activation energy

• Gibbs free energy

The entropy change for the dissolution of calcium chloride in water shown at the side might be expected to be positive, but the actual ΔS is negative. Which of the following is the most plausible explanation for the net loss of entropy during this process?

• CaCl₂ (s) is an amorphous solid.

• The particles in the solution are more ordered than the particles in the

  solid.

• The ions in solution can move more freely than the particles in the

  solid.

• The decreased entropy of the water molecules in the solution is greater

  than the increased entropy of the ions.

• In solution, the distance between ions is much greater than the distance

  between the ions in the solid.

Which of the following best describes the role of a spark in a butane lighter?

• The spark decreases the activation energy of the combustion reaction.

• The spark increases the concentration of butane in the reaction chamber. 

• The spark provides the heat of vaporization for the liquid fuel. 

• The spark supplies some of the energy to form the activated complex for the combustion reaction. 

• The spark provides an alternative stoichiometry for the reaction, decreasing the amount of oxygen required for complete combustion.

Which of the following processes demonstrates a decrease in entropy (ΔS < 0)?

• Br (s) → Br (l)

•  I₂ (s) → I₂ (g) 

• Combining equal volumes of C₂H₆O₂ (l) and H₂O (l) 

• The precipitation of PbI₂ from solution. 

• The thermal expansion of a helium balloon.

A student adds solid ammonium chloride to a beaker containing water at 25°C. As it dissolves, the beaker feels colder. Which of the following are true regarding the ΔH and ΔS of the dissolution process of NH₄Cl(s)?

• ΔH > 0,ΔS > 0

• ΔH > 0, ΔS < 0

• ΔH = 0, ΔS = 0

• ΔH < 0, ΔS > 0

• ΔS < 0, ΔS < 0

The normal melting point of Ag(s) is 962°C. Which of the following is true for the process represented below at 962°C?

Ag (s) <-> Ag (l)

• ΔH =0

• ΔS = 0

• TΔS = 0

• ΔH =TΔS

• ΔH > TΔS

The enthalpy of combustion of ethanol (C₂H₅OH (l)) is shown above. Using this information and the data in the table above, the standard heat of formation of CO₂ (g) is closest to:

• –1,080 kJ mol⁻¹ 

• –540 kJ mol⁻¹ 

• –510 kJ mol⁻¹

• –390 kJ mol⁻¹

• –250 kJ mol

What is the standard enthalpy change, ΔH⁰_rxn, of the reaction represented at the side? 

• –24.3 kJ

• –58.3 kJ

•  24.3 kJ 

• 58.3 kJ

• 77.7 kJ

When CO₃ (s) is added to a beaker of dilute HCl (aq) at 298 K, the beaker gets cold and a gas is produced. Which of the following indicates the correct signs for ΔG, ΔH, and ΔS for the reaction represented above?

 Answer in this manner

ΔG, ΔH, ΔS

•  -         -        -

•  -         -       +

• +         -       -

• -         +      +

• +        +      +