# chemistry

posted by .

A sample of 1.00 mol H2O(g) is condensed isothermally and reversibly to liquid water at 100°C. The standard enthalpy of vaporization of water at 100°C is 40.656 kJ mol−1. Find w, q, ∆U, and ∆H for this process.

-------------
I can solve for ∆H: n * standard ∆H * -1 because reverse of vaporization.
-40.656 kJ

I can solve for ∆U:
∆H = ∆U + ∆n(gas)*RT
-40.656 = ∆U + -1 * -R * 373.15K
∆U = -37.55 kJ

Now, how do I figure out w and q

I know that
∆U = q + w
but beyond that, how do I solve?

• Chemical Engineering -

The pressure is constant, and so the heat at constant pressure is qp = - dH vaporization. W=-pdV and so since p=pext=1atm and dV = (vf - vi) = vliquid - vvapor, we'll say that since the volume of the vapor is significantly greater than that of the liquid, then vf-vi is approximately equal to -volume of vapor = - nRT/pext. Solve for these and then you get dU.

• chemistry -

Well, the pressure here is not constant, but the temperature is. Reversible implies that there are infinitesimal changes in certain parameters.
For isothermal, reversible systems

delta H=0
delta U=0
q=-w
and w=-nRTln(Vf/Vi)

You can find your Vf by using the density constant for liquid water which s essentially 1.0 g/mL.
I used SATP laws for an ideal gas to find the volume of water at room temp. Then I converted to the volume at higher temp using the relation V1/T1=V2/T2. Hope this works.

## Similar Questions

1. ### chemistry

Calculate the heat of formation of water from its constituent elements from the following information: 3 H2 (g) + O3 (g) ¨ 3H2O ∆H = ?
2. ### Chemistry

1.What is the molar heat of vaporization of water, given the following thermochemical equations?
3. ### chemistry

7. (a) Determine the crystal lattice energy for LiF(s) given that the ∆Hsubl for Li = 155kJ/mol, ∆H0f for F(g) = 78.99kJ/mol, IE1 of Li = 520kJ/mol, EA for Fluorine = -322kJ/mol and the ∆H0f LiF(s) = -589.5kJ/mol …
4. ### chemistry

3.5 moles of steam at 100 C are condensed at 100 C and the resulting water is cooled to 42.3 C. Calculate the entropy change for this process.(The molar heat capacity of liquid water is 75.3 J mol1 K1, and the molar enthalpy of vaporisation …
5. ### AP Chemistry

A 34.05 gram liquid sample of an unstable compound is deposited in a metal piston assembly that has a cylinder with a diameter of 20.0 cm. After the sample is added, the piston is placed in contact with the liquid and the piston vent …
6. ### Chemistry - Science (Dr. Bob222)

Hydrazine is used as a rocket fuel because its reaction with oxygen is extremely exothermic: N2H4(liquid) + O2(g)  N2(g) + 2H2O(liquid) ΔH(reaction) = -615 kJ mol-1 What is the enthalpy of this reaction if water were produced …
7. ### chemistry

Calculate the standard entropy change for the reaction of calcium oxide with water to form calcium hydroxide: CaO(s) + H2O(ℓ) → Ca(OH)2(s) at 298 K. ∆S ◦ m ∆H◦ f J K·mol?
8. ### chemistry

What is the ∆G for the following reaction under standard conditions (T = 298 K) for the formation of NH4NO3(s)?
9. ### Chemsitry

What is the ∆G for the following reaction under standard conditions (T = 298 K) for the formation of NH4NO3(s)?
10. ### AP Chemistry

DrBob222 PLEASE HELP Hf of CO2 = -393.5 kJ/mol Hf of H2O = -285.8 kJ/mol The combustion reaction for benzoic acid C6H5CO2H(s) + 15/2 O2(g) → 7 CO2(g) + 3 H2O(ℓ) has ∆H0 = −3226.7 kJ/mole. Use Hess’s Law to …

More Similar Questions