Question

Show all work for full credit. RATATemperature: a95% aa't a78 = a95 K Room Temperature: Observations of liquid Unknowns: Unknown A Unknown B Unknown C Unknown D Unknown E T(K) Time(s) T (K) Time(s)T(K) Time(T (K) Time(s) T (K) Time(s) 82.4 nun. amin 1292. 31 mun30 92 mn nun anun 30sec 303 9 I Heat of Vapo and Intermolecular Forces: Post-Lab POST-LAB QUESTIONS Show all work for full credit. 1. Some of the temperatures dropped very quickly as the solution evaporated and some dropped very slowly. Relate this rate of evaporation to the strength of the intermolecular forces. Explain your reasoning. 2. The process of recording temperature versus time as completed in this experiment is similar to the process used in calorimetry. That process can be used to directly calculate the enthalpy of a system. Why couldn't you calculate the enthalpy of chis system directly using the data you collected?

Answer 1

1. The greater the strength of the intermolecular forces of attraction, the more difficult it will be for the surface molecules to break apart and get converted to vapours, the slower will be the temperature drop. So the rate of evaporation is inversely proportional to the strength of intermolecular forces of attraction. Greater the strength of the intermolecular forces of attraction, lesser the rate of evaporation.

2. In calorimetry, it is assumed that there is no heat lost to or gained from the surroundings. For example, if a heated metal is dropped in cold water in a calorimeter, the temperature of the water is raised and temperature of metal drops. The process is carried out in a calorimeter which is considered to be a isolated system. In given method, it is not an isolated system, there can be heat lost to or gained from surroundings. So calorimetry is used to calculate enthalpy of a system and not the given method.