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107 grams of liquid water are in a cylinder with a piston maintaining 1 atm (101325 Pa) of pressure. It is exactly at the boiling point of water, 373.15 K. We then add heat to boil the water, converting it all to vapor.

The molecular weight of water is 18 g/mol and the latent heat of vaporization is 2260 J/g.

1) How much heat is required to boil the water?

2) Assume that the liquid water takes up approximately zero volume, and the water vapor takes up some final volume Vf. You may also assume that the vapor is an ideal gas. How much work did the vapor do pushing on the piston?

3) How much did the water internal energy change?

User Jaseelder
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2 Answers

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Final answer:

To boil the water, approximately 1.31 x 10^6 J of heat is required. The work done by the vapor pushing on the piston is approximately 0.021 atm*m³. The change in internal energy of the water is approximately 1.31 x 10^6 J.

Step-by-step explanation:

To calculate the amount of heat required to boil the water, we first need to calculate the mass of the water. Since the molecular weight of water is 18 g/mol, we can divide the given mass of 107 grams by the molecular weight to get the number of moles. So, 107 g / 18 g/mol = 5.94 mol.

Next, we need to calculate the heat required to vaporize the water. The latent heat of vaporization is given as 2260 J/g. So, the heat required is 5.94 mol * 2260 J/g * 107 g/mol = 1.31 x 10^6 J.

To calculate the work done by the vapor, we can use the ideal gas law. The volume of the vapor is given as Vf. The ideal gas law is PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant, and T is the temperature in Kelvin. Since the pressure is constant and equal to 1 atm, we can rewrite the equation as V = (nRT)/P. Plugging in the values, V = (5.94 mol * 8.314 J/mol*K * 373.15 K) / 101325 Pa = 0.021 m³.

To calculate the work done by the vapor, we can use the formula W = PΔV, where W is the work done, P is the pressure, and ΔV is the change in volume. Plugging in the values, W = 1 atm * 0.021 m³ = 0.021 atm*m³.

The change in internal energy of the water can be calculated using the first law of thermodynamics, which states that ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added, and W is the work done. Plugging in the values, ΔU = 1.31 x 10^6 J - 0.021 atm*m³ = 1.31 x 10^6 J - 2.13 J ≈ 1.31 x 10^6 J.

User Rahul Kalidindi
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1 vote

Answer:

Step-by-step explanation:

1.)


Q=mL\\\\=107g * 2260J/g\\\\=241.82KJ

2.)


Moles=(m)/(M)=(107g)/(18g)=5.944moles

using
PV=nRT\\\\V_f=(nRT)/(P)\\\\V_f=(5.944* 8.314* 373.15)/(101325)\\\\=0.182m^3

At constant pressure


W=Pa(\bigtriangleup V)\\\\Pa(V_f-0)=PaV_f\\\\=101325* 0.182=18.44KJ

3.)


Q=\bigtriangleup U + W\\\\\bigtriangleup U=Q-W=241.82-18.44=223.38KJ

User Ngoctranfire
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