Question

1-Suppose a Styrofoam cup that weighs 5 grams was used for this experiment in place of the aluminum calorimeter. What differences in the analysis and results might you expect? The specific heat of Styrofoam is 0.3 kcal/kg-°C (0.3 cal/g-°C) and its thermal conductivity is 0.00008 cal/sec-cm-°C.

2- What amount of heat per unit mass must be removed from water at 0°C to change it back to ice?

Answer 1

1.a) Heat loss - aluminium conducts heat much more effectively than styrofoam. This means that the aluminium calorimeter will carry the heat of the reaction away from the reaction vessel to the outside world faster than styrofoam will.

b)Heat absorption - The calorimeter gets heated up along with the reaction mixture. A calorimeter that absorbs large amounts of energy will have a relatively lower final temperature, since more of the reaction's heat went into heating up the calorimeter than went into heating up the reaction mixture. This quantity is known as the calorimeter constant and varies depending on the materials and mass of the calorimeter. Styrofoam absorbs more heat per gram than aluminium, but the aluminium calorimeter is heavier. With a fast reaction there is the additional fact that the styrofoam calorimeter probably never comes up to the full temperature of the reaction before you quit recording temperatures. Thus leading to a small source of lost heat for the aluminium calorimeter as compared to the styrofoam.

2. q1 = heat required to melt the ice to water at 0.00 °C.

q1=mΔHfus=1×334J/1g = 334 J

this is the heat required to melt ice to water

and thus the opposite of it will be the heat per unit mass required to convert water to ice

that is negative of 334 J= (-344 J).