Physical Chemistry (I) - Quiz 2

1. A chemical reaction takes place in a container of cross-sectional area 50.0 cm².  As a result of the reaction, a piston is pushed out through 15 cm against an external pressure of 121 kPa. Calculate the work done by the system.

2. A sample consisting of 2.00 mol He is expanded isothermally at 22°C from 22.8 dm³ to 31. 7 dm³ (a) reversibly, (b) against a constant external pressure   equal to the final pressure of the gas, and (c) freely (against zero external pressure). For the three processes calculate q, w, ΔU, and ΔH.

 3. A sample of 2.00 mol CH₃OH(g) is condensed isothermally and reversibly  to liquid at 64°C. The standard enthalpy of vaporization of methanol at 64°C is 35.3 kJ mol^-1. Find w, q, ΔU, and ΔH for this process.

4.  The standard enthalpy of formation of phenol is -165.0 kJ mol^-1.

Calculate its standard enthalpy of combustion.

                 C₆H₅OH(l) + 7O₂(g)  → 6CO₂(g) +  3H₂O(l)

Δ_fH^Φ (CO₂) =  -393.15 kJ mol^-1

Δ_fH^Φ (H₂O) =  -285.83 kJ mol^-1

Δ_fH^Φ (O₂) = 0 kJ mol^-1

5. From the following data, determine Δ_fH^Φ for

                            2 B(s) + 3H₂(g) → B₂H₆(g),  at 298 K:

 (1)   B₂H₆(g)  + 3 O₂(g)  → B₂O₃(s) + 3 H₂O(g)            Δ_fH^Φ=  -1941 kJ mol^-1

(2)   2 B(s) + 3/2 O₂(g)  → B₂O₃(s)                               Δ_fH^Φ=  -2368 kJ mol^-1

(3)   H₂(g)  + + 1/2 O₂(g)  → H₂O(g)                            Δ_fH^Φ=  -241.8 kJ mol^-1