A one mole piece of iron is placed in a container with dilute hydrochloric acid

Question

A one mole piece of iron is placed in a container with dilute hydrochloric acid covered by a piston. The container is placed in a heat reservoir (water) that fixes the temperature. The iron reacts isothermally with the hydrochloric acid according to the reaction a) The production of hydrogen gas pushes the piston up. The atmospheric pressure is one atmosphere and the temperature is 27 Degree C. How much work is done by the surroundings? If the reaction proceeds very slowly, how much work is done by the system? What can you say if the reaction proceeds very quickly. (10 pts) b) Et is found that the reaction is exothermic and that 180 kJ of heat is transferred to the surroundings. What is the reaction enthalpy AH? What is Delta U? (10 pts) c) Same two questions for the case that the container is kept at a fixed volume. (15 pts)

Explanation / Answer

a) PV = nRT

here P= 1 atm , n=1 mol, T=27oC= 27+273=300K

So, V= nRT/P= 1*0.0821*300/1= 25.42L

This is V final. Vinitial= 1L

? V =25.42-1-24.42LKj

Work done by the system= -P? V= -1*24.42= 24.42KJj

if reaction proceed very fast, w= 2.303nRTlogV2/V1= 2.303*1*0.0821*300 log24.42/1 = 78.67 Kj

b)the reaction is exothermic, So ?H= -180 KJ

?H= ?U+?ngRT

?ng=1-0=1

-180 =?U+1*8.314*300

?U=-2674.2 KJ/mol

c) According to first law of thermodynamics;

q= ?U+P?V

If the process is carried at constant volume, ?V=0

q=?V, internal energy change is equal to the heat evolve or absorb.

?H=?U+P?V

if ?V=0, then ?H=?U

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