EXPERIMENT 12 MEASUREMENT OF SOME THERMODYNAMIC VALUES OF ICE Introduction Therm

Question

EXPERIMENT 12 MEASUREMENT OF SOME THERMODYNAMIC VALUES OF ICE Introduction Thermodynamics is useful because it allows predictions about whether a reaction will occur under a given set of conditions. Thermodynamics studies the energy changes that occur during reactions by measuring the initial and final values of several important properties called state functions. A state function is a property that has a definite, fixed, value for each state of the system. Examples of state functions are Enthalpy, Entropy and Gibbs' Free Energy. When a system is altered, the change in the value of the state function depends only on the initial and final states and not on how the change was accomplished. show how much heat is exchanged when a reaction is carried out under constant Enthalpy changes pressure. Entropy changes give information about the degree of randomness and Gibbs free energy changes provide a measure of the system's ability to do useful work. degree of randomness and Gibbs' free ener gy In this experiment, the enthalpy change associated with the melting of ice, AHs, will be determined: H2O(s) H2O(1) change of melting, ASfus, and the Gibb's free energy change of melting, Gfus, can From this, the entropy change of melting, ASfus, and the Gibb's free energy be derived. ulate the enthalpy of fusion, it is necessary to measure the amount of heat a given sample of ice To calc must absorb in order to melt.

Explanation / Answer

1. If we do not remove the cold water from the ice before adding it to warm water, then the mass of that water will add up to the warm water present and would be less than the mass of dry ice. So,amount of heat which is gained by dry ice would be different from this wet ice and all the calculations would be wrong. The main motive of the experiment is to measure heat lost by warm water and heat gained by cold water. If the measurements are wrong, then calculations would be also wrong.

2. It is necessary to extrapolate the post melting line, because we want to know the instant temperature at the time of mixing. While in taking the readings, It increases and then it becomes constant. So, that measurement is after some time of mixing. But to determine temperature diference, we extrapolate it to the point when we mixed both cold and warm water. That is why it is important to extrapolate the post-melting line. The same reason is valid for not taking the lowest temperarure.

3. When we take out the ice from freezer, the temperature of the ice is less than zero. That is why we keep it for some time, before adding it to the exerimental set up. In the calculations, we say that the temperature of the ice is 0 oC, so if the temperature of the ice is actually -20°C, then it would give wrong readings. The heat lost by warm water would be used to heat the ice from its freezing temperature to 0 oC first, so heat is lost which we do not consider in calculations.

4. While doing the calculations, we assume that the temperature of the ice is 0 oC, because conventionally we say that the temperature of ice is 0 oC but we do not measure it in experiment.

We also extrapolate the graph and assume that the temperature at mixing can be found by extrapolation. But we do not know about it.

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