Thermodynamics problem. Please help!!

Question

 A student takes a Styrofoam cooler in fills it with 2.00 L of water. He then adds a small amount of sodium to it and it reacts according to the equation below. The initial temperature of the water is room temperature, 23.9°C, and the temperature of the water after the reaction is complete is 25.8°C. The reaction takes place at 0.987 atm pressure  and produces 1.968 L of hydrogen gas.

 

2Na(s) + 2 H2O(l) -> 2Na(aq) + H2(g)

 

1. Determine the amount of heat absorbed or released by the reaction. 

2.   Calculate the work for this reaction. 

Answer 1

2Na(s) + 2 H2O(l) -> 2Na(aq) + H2(g)

heat = q = mC∆T

where m is mass of water = 2 kg assuming a density of 1g/ml

C = specific heat of water = 4.184 kJ/kg/deg

∆T = change in temperature = 25.8º - 23.9º = 1.9º (note positive value so this is an exothermic reaction, i.e. heat is released)

 

q = (2.00 kg)(4,184 kJ/kg/deg)(1.9 deg) = 15.9 kJ energy released

 

work = -P∆V at constant pressure = -(0.987 atm)(1.968 L) = -1.942 L-atm

-1.942 L-atm x 101.325 J/L-atm = -197 J = work done by the system on the surroundings (as indicated by the - sign)