Can someone please help me with these two problems? 1) It is recommended that ho
ID: 979115 • Letter: C
Question
Can someone please help me with these two problems?
1) It is recommended that home refrigerators maintain an internal temperature of around 40° F for safe food storage. Assuming that the typical refrigerator operates at 20% of the ideal efficiency and that electricity costs $0.10 / (kW hr), what is the annual cost of operation in a 70° F room if the door is opened 10 times a day with an average heat gain per opening of 200 kJ? How much would it cost to keep the inside at 35° F?
2) Calculate Srxn0 (per mole as written) for the water splitting reaction at 330 K:
2 H2O(l)------>2H2(g) + O2(g)
Explanation / Answer
Internal temperature = 40oF
Assume 20% of ideal efficiency and cost of electricity = $0.10/ kW hr.
40 x 20% x $0.10 = $32
The annual cost for 70oF
70 x $32 /10 = $224
For 35oF
35 x 20% x $0.10 = $24.5
The so-called "hydrogen economy" is based on H2(g) produced from water by solar energy. The gas is then burned as fuel: 2H2(g) + O2(g) ® 2H2O(l)
One simple way to reverse the binding is to increase the temperature, so that at low temperature the equilibrium lies to the right and at high temperature to the left. Use this information, plus any chemical knowledge or intuition to infer the sign of DG, DH and DS at "low" and "high" temperatures. (You may assume that DH and DS do not change greatly with temperature.)
At low temperature, the equilibrium lies to the right favouring products: G < 0. At high temperature, it lies to the left favouring reactants: G > 0. The reaction involves formation of a solid from a solid and a gas. There is therefore a decrease in the entropy: S < 0. This is true at all temperatures. The forward reaction becomes less favourable as the temperature is increased. Le Chatelier’s principle therefore suggests that the reaction is exothermic: H < 0. This is true at all temperatures. (If the temperature is increased, the equilibrium shifts to remove heat by increasing the backward reaction.)