REFLECTION JOURNAL ON TEST 2
Test 2 for the Principles of Chemical Processes II subject was held on 8 Nov 2012. This time, Test 2 covers CO1 and CO3 (course outcome) which are :-
- CO1 : ability to write basis, references conditions and carry out unit conversion and equipment identification for various chemical processes, process variables and unit operations in chemical industry.
- CO3 : ability to calculate the standard heat of reactions using Hess’s Law, heat of formation and heat of combustions and then solve problems for reactive process.
Firstly, Question 1 was asked to calculate the standard heat of reaction for the combustion of liquid n-pentane at 25oC with water product in liquid form. So, the chemical equation for the production water liquid as follows :
C2H12 (l) + 8 O2 (g) ----------> 5 CO2 (g) + 6 H2O (l)
I just take an easy way to solve without noticed that I should do hypothetical path first to solve this question. So, the correct solution for the standard heat of reaction for the combustion of liquid n-pentane to form liquid water is equal to the summation of heat of vaporization of C2H12 (l), heat of combustion of C2H12 (g) and of heat of vaporization of H2O (g).
Secondly, Question 2 was asked to determine the standard enthalpy change for this reaction, 2 C (s) + 2 H2O (g) ----------> CH4 (g) + CO2 (g), from the given standard enthalpies of reaction. In the lecture class, we were taught to calculate the standard heat of reaction using 3 methods which are using Hess’s Law, heat of formation and also heat of reaction (combustion) as stated on above explanation (CO3). For this question Hess’s Law method is the most suitable method to use.
Thirdly, Question 3 was required us to perform mass balance to solve the problem which carry about 5 marks from the total marks of this question which is 30 marks. It is look simple to answer it since it only 5/30 marks, but if the students failed to perform mass balance the next sub-questions will be affected when we have to calculate the standard heat of reaction then. This situation happened to me on Question 4 and I lost a lot of marks there.
Question 3 and 4 are look alike. The difference is Question 3 asked to calculate the amount of heat produced using the heat formation method while Question 4 asked to calculate the heat transfer using heat of reaction method. The other difference is the fractional conversion for the reaction in Question 3 is 100%. Instead, Question 4’s fractional conversion for the reaction is 65%. The term “100% excess air” made me confused at that time. As a result, my mass balance was wrong except for the SO3 and SO2 balance.
In conclusion, the whole Test 2 is quite okay compared to the last test. But, still below the par 
. The next test will covers CO1 and CO4.