A system has 75 J of work done on it, and its internal energy increases by 100 J. Which statement correctly describes the heat transferred?

A gas in a piston–cylinder is compressed from 5 L to 3 L against a constant external pressure of 4 atm. Using the chemistry sign convention, what is the work done on the gas?

A sample in a piston–cylinder expands from 10.0 L to 15.0 L as water vaporizes against a constant external pressure of 3.0 atm. Using the chemistry sign convention, what is the pressure–volume work on the system?

A water sample absorbs 4.20 × 10² J of heat as its temperature rises from 30.0 °C to 35.0 °C. What is its mass? Use c = 4.20 J/(g·°C) and report the result with the appropriate significant figures.

How much heat is required to raise the temperature of 45.0 g of NaCl from 35.0 °C to 60.0 °C? Use c = 0.900 J/(g·°C) and report three significant figures.

Which statement expresses the second law of thermodynamics for a spontaneous process?

For a process at constant pressure with only pressure–volume work, which statement is consistent with a positive enthalpy change, ΔH > 0?

Which process is endothermic?

For the combustion reaction below, ΔH° = −1,255 kJ per mole of C₂H₂ reacted. How much heat is released when 2 mol of acetylene reacts?
C₂H₂(g) + 5/2 O₂(g) → H₂O(g) + 2CO₂(g)

How many grams of NH₃ react with excess O₂ when 150 kJ of heat is released? Use the enthalpy change for the reaction as written.
4NH₃(g) + O₂(g) → 2N₂H₄(l) + 2H₂O(l), ΔH = −300 kJ

Use Hess’s law to calculate ΔH for 2A + B → 5D + 2E. Each enthalpy below is given per mole of reaction as written.
A + B → 2C + D, ΔH = +100 kJ/mol
2D + E → ½A + C, ΔH = −20 kJ/mol

Use the two reactions below to express ΔH° for 2CO(g) + O₂(g) → 2CO₂(g).
2C(s, graphite) + O₂(g) → 2CO(g), ΔH₁
C(s, graphite) + O₂(g) → CO₂(g), ΔH₂

Estimate the enthalpy change for the gas-phase reaction using the average bond dissociation energies in the table.

Which processes have a positive entropy change for the system, ΔS_sys > 0?
I. NaCl(s) dissolves to form Na⁺(aq) and Cl⁻(aq).
II. 6CO₂(g) + 6H₂O(l) → C₆H₁₂O₆(s) + 6O₂(g).
III. CO(g) + 2H₂(g) → CH₃OH(l).
IV. C₄H₁₀(l) → C₄H₁₀(g).

For the same amount of AB at the same temperature, which listed change gives the greatest increase in entropy?

An exothermic dissolution transfers heat to finite surroundings with a positive heat capacity. Assume the surroundings do not undergo a phase change. What are the signs of the temperature and entropy changes of the surroundings?

For a closed system undergoing a spontaneous process at constant temperature and pressure with only pressure–volume work, which statements are correct?
I. The total energy of the system and surroundings is conserved.
II. The total entropy of the system and surroundings increases.
III. ΔG for the process is negative.
IV. A process with ΔH < 0 and ΔS_sys > 0 is spontaneous at any T > 0, assuming these signs remain unchanged.

Which statements are correct? For statements II–IV, assume constant temperature and pressure and only pressure–volume work.
I. At 298.15 K in the gas phase, n-butane, CH₃CH₂CH₂CH₃, has a greater standard molar entropy than propane, CH₃CH₂CH₃.
II. ΔG > 0 means the forward process is nonspontaneous.
III. If ΔH > 0 and ΔS_sys < 0, then ΔG > 0 at T > 0.
IV. At equilibrium, ΔG = 0.

At which listed temperature is the reaction spontaneous if ΔH = +5.0 kJ/mol and ΔS = +20 J/(mol·K)? Assume ΔH and ΔS are constant over this temperature range.