Answer:
a. 478.69 K
b. 939.43 
 
c. 19.30 J
d. 64.5J
Explanation:
From the question, we can identify the following;
 = 785
 = 0.000785 
 = 400K
 = 125 Kpa =  125 000 Pa
Using the ideal gas equation,
 PV = nRT
where R is the molar gas constant = 8.314 
⋅Pa⋅
⋅
Thus, n = PV/RT = (125000 × 0.000785)/(8.314 × 400) = 0.03 mol
a. Steam temperature in K
To calculate this, we use the constant pressure process;
q = nΔH
 Where q is 83.8J according to the question
Thus;
83.8 = 0.03 × [34980 + 35.5
 - (34980 + 35.5
)]
83.8 = (0.03 × 35.5) (
 - 400K)
83.8 = 1.065 (
  - 400)
78.69 = (
  - 400)
 = 400 + 78.69
  = 478.69 K
b. Final cylinder volume
To calculate this, we make use of the Charles' law(Temperature and pressure are directly proportional)
/
 = 
/
  =  
/
   = (785 × 478.69)/400
   = 939.43 
 
c. Work done by the system
Mathematically, the work done by the system is calculated as follows;
w = P(
- 
) = 125 KPa ( 939.43 - 785) = 19.30 J
d. Change in internal energy of the steam in J
ΔU = q - w = 83.8 - 19.3 = 64.5J