Question

Calculate the energy released when 50.0g of steam condenses at 100℃.

Use the cooling curve to show what happens when 50.0g steam condenses at 100℃ and then cools to 20℃. Then calculate this energy change.

6. Use the below cooling curve for water for the following questions. 

A. Label the melting/freezing point. 

B. Label the boiling/evaporation point. 

C. At what state is water when the temperature is 80 °c? 

D. At what state is water when the temperature is -20 °C? 

E. What happens to the temperature of water when energy is removed from water at 70°C? 

F. What happens to the temperature of water when energy is removed from water at 100 °C? 

G. Label the points on the plot where each of the following constants are used to determine the calories associated with a change in heat. Hlas, Hvap, Specific Heat (SH or c) 

H. Calculate the energy released when 50.0 g of steam condenses at 100 °C. 

I. Use the cooling curve to show what happens when 50.0 g steam condenses at 100 °C and then cools to 20 °C. Then calculate this energy change. 

Answer 1

For the labeling parts (A, B, G):

140 120 100 80 Temp. 60 40 20 C) 20 Hvap Boiling Point Freezing Point Hfus Heat Removed

For letter C, water is on a liquid state at 80^oC as it is between the freezing and boiling point.

For letter D, water is on a solid state at -20^oC as it is after the freezing point.

For letter E, temperature drops from 70^oC when energy is removed, as there is no change in state.

For letter F, temperature remains the same at 100^oC when energy is removed until gas changes to a liquid state.

For letter H:

Heat of vaporization of water is 44 kJ / mol

We turn the 50 grams to moles with the molar mass:

50 g * (1 mol / 18 g) = 2.78 moles

So the energy released will be:

Q = 2.78 * 44 = -122.32 kJ (negative sign as it is heat released)

For letter I, we add the heat change of water from 100 to 20 degrees using the heat capacity of water:

Q = -122.32 kJ + (50g * 4.14 J/g^oC * (20-100)^oC)*(1 kJ / 1000 J)

Q = -122.32 + (-16.56) = -138.88 kJ