All oxides of sulfur (SO, SO₂, and SO₃) have negative ΔG°_f at 25°C but only one oxide has a positive ΔH°_f at the same temperature. Identify the oxide and explain why its ΔH°_f is positive.

The reaction of isobutylene (C₄H₈) with ethanol (C₂H₆O) produces ethyl tert-butyl ether (C₆H₁₄O).

ΔH°_{f, C6H14O} = —350.8 kJ/mol

ΔH°_{f, C2H6O} = —269.29 kJ/mol

ΔH°_rxn = —4044 kJ/mol

What is the ΔH°_f for isobutylene in kJ/mol?

Diisopropyl ether is a compound used as a solvent in paint thinners and stain removers. A 0.2150 g sample of diisopropyl ether was burned in excess oxygen which produced 0.5557 g CO₂(g) and 0.2654 g H₂O(l). A separate sample of diisopropyl ether vapor was placed in a 1.00 L vessel at 70.5°C and had a final pressure of 98.0 kPa. The mass of the vessel increased by 3.504 g.

If the enthalpy of combustion of diisopropyl ether is ΔH°_c = –4010.1 kJ/mol, calculate its standard enthalpy of formation (ΔH°_f).

Calculate the heat produced when 2.000 mol of butane gas (C₄H₁₀) combusts and produced CO₂ and H₂O under standard conditions.

When potassium chloride (KCl) dissolves in water to form K⁺ and Cl^– ions, the temperature of the solution decreases.

KCl(s) → K⁺(aq) + Cl^–(aq) 

Identify which has a higher enthalpy, KCl(s) or the K⁺ and Cl^– ions.

Copper reacts with dilute nitric acid to produce copper nitrate, nitrogen dioxide and water:
Cu(s) + 4 HNO₃(aq) → Cu(NO₃)₂(aq) + 2 NO₂(g) + 2 H₂O(l)
A 0.215 g piece of copper metal was mixed with a sufficient amount of dilute nitric acid to produce 100.0 mL solution in a coffee-cup calorimeter. Due to the exothermic reaction, the temperature of the mixture increased from 23.0°C to 25.5°C. Calculate the value of ΔH°_rxn for this reaction. (Take d = 1.0 g/mL and C = 4.18 J/g•°C)

Using the information from the table below, calculate the ΔH°_rxn for the reaction of ammonia and oxygen to produce nitric oxide and water vapor.

4 NH₃ + 5 O₂ → 4 NO + 6 H₂O