Introduction:

Energy is used in any type of reaction that causes a substance to change its phase. When heating a solid, energy is put into the substance, causing the substance to gain energy. If heating continues on the solid, a phase transition will occur and the solid will melt to a liquid. The amount of heat required to melt a solid to a liquid is an enthalpy, and is called heat of fusion. If the heating continues on the liquid, the substance will then reach its boiling point, and a phase change will occur again from a liquid to a gas. When a phase change from a liquid to a gas occurs, the change is known as the heat of vaporization. In some cases, a substance converts straight from a solid to a gas, called the heat of sublimation.

In the lab, each group conducted experiments to determine the heat of fusion of ice, the heat of vaporization of nitrogen, and the heat of sublimation of CO2 (dry ice).

Results:

Observations and Data:

Part 1:

Table 1: Mass of Nested Pairs of Styrofoam Cups

Pair 1 Pair 2
3.63 g 3.73 g

 

Table 2: Heat of Fusion of Ice to Water

Quantity Trial 1 Trial 2 Trial 3
m[H2O (l)] 51.2 g 46.8 g 59.3 g
m[H2O (s)] 20.0 g 21.1 g 22.6 g
Ti[H2O (l)] 54.0° C 50.0° C 57.0° C
Ti [H2O (s)] 0.00° C 0.00° C 0.00° C
Tf[H2O (l & s)] 20.0° C 19.9° C 28.3° C
ΔT[H2O (l)] -34.0° C -30.1° C -28.7° C
ΔT [H2O (s)] 20° C 19.9° C 28.3° C
ΔHfus[H2O (l)] 8 kJ/mol 7 kJ/mol 8 kJ/mol

 

Part 2:

Table 3: Heat of Vaporization of Liquid Nitrogen to Gas

Quantity Trial 1 Trial 2 Trial 3
m[H2O (l)] 63.1 g 58.7 g 61.4 g
m[N2 (l)] 41.0 g 40.9 g 39.0 g
Ti[H2O (l)] 57.0° C 58.2° C 60.5° C
Tf[H2O (l)] 29.1° C 26.3° C 29.5° C
ΔT[H2O (l)] -27.9° C -31.9° C -31.0° C
ΔHvap[H2O (l)] -5.0 kJ/mol ____ kJ/mol ____ kJ/mol

 

Part 3:

Table 4: Heat of Sublimation of CO2

Quantity Trial 1 Trial 2 Trial 3
m[H2O (l)] 59.4 g 62.6 g 52.6 g
m[CO2] 15.2 g 15.0 g 15.7 g
Ti[H2O (l)] 54.9° C 54.9° C 60.3° C
Tf[H2O (l)] 19.0° C 19.1° C 17.9° C
ΔT[H2O (l)] 35.9° C 35.8° C 42.4° C
ΔHsub[H2O (l)] 26.9 kJ/mol ____ kJ/mol ____ kJ/mol

 

Sample Calculations:

Energy-of-Phase-Changes-Calculations

Discussion:

To determine the heat of fusion, the group heated 250 mL of water to approximately 55°-65° C. Then, 60 mL of the heated water was poured into one pair of nested Styrofoam cups. The initial mass was recorded. Then, 20 g of ice was added to the heated water. The initial and final temperatures were recorded, as well as the final mass. This process was repeated two times to ensure repetition and accurate results.

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