1. Calculate the heat (in joules) adsorbed by the system for each of the followi
ID: 938538 • Letter: 1
Question
1. Calculate the heat (in joules) adsorbed by the system for each of the following examples (the system is given in italics). Specify the sign of the heat. (a) 100 g of liquid water is heated from 0o C to 100 o C at 1 bar. (b) 100 g of liquid water is frozen to ice at 0o C and 0.01 bar. (c) 100 g of liquid water is evaporated to steam at 100 o C at 1 bar.
2. An ice cube weighing 18 g is removed from a freezer, where it has been at –20o C. (a) How much heat is required to warm it to 0o C without melting it? (b) How much additional heat is required to melt it to liquid water at 0o C?
3. Consider the reaction in which 1 mol of aspartic acid(s) is converted to alanine(s) and CO2(g) at 25o C and 1bar pressure. The balanced reaction is (NOTE FROM SRB: There is an error in the reaction in some versions of the textbook. The correct reaction is below.): NH3 + CH(CH2COOH)COO- (s) CH3CHNH3 + COO- (s) + CO2 (g) (a) How much heat is evolved or absorbed? (b) Write a cycle you could use to calculate the heat effect for the reaction at 50o C. State what properties of molecules you would need to know and what equations you would use to calculate the answer.
4. One mole of an ideal monatomic gas is expanded from an initial state at 3 bar and 450 K to a final state at 2 bar and 250 K. (a) Choose two different paths for this expansion, specify them carefully, and calculate w and q for each path. (b) Calculate U and S for each path.
Explanation / Answer
1) a) heat absorbed = mCp (T2-T1)
= 100g * 4.18 J/(g°C) * (100 - 0) = 4.18 X 10^4 J
b) heat absorbed = 0 (no temperature change)
c) heat absorbed = 0 (o temperature change)
2. heat absorbed = mCp (T2- T1)
= 18g * 4.18 J/(g°C) * (0 + 20)
=1504.8 J
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