[azzarn]

Hey all, This is a problem I have tried repeatedly, and am confident of my solution, yet it differs from the book answer. I'm hoping that some of you can try the problem and post your solution, so I can finally prove my chem teacher is wrong about something. For that reason, I will not influence how to do the problem, just the question and needed numbers.

Calculate the amount of heat involved in condensing 100.00g of benzene gas (C₆H₆) at 80.00 degrees celsius to liquid benzene at 25.00 degrees celsius.
Specific Heat:1.72
Boiling Point:80 celsius
Heat of Vaporization:30.8

Good Luck, and please show work. (I know it is hard on a computer)

[lancenti]

We need the units, whether it's J/K or kJ/K, kCal/K makes a difference.

[Borek]

Hey all, This is a problem I have tried repeatedly, and am confident of my solution, yet it differs from the book answer. I'm hoping that some of you can try the problem and post your solution, so I can finally prove my chem teacher is wrong about something. For that reason, I will not influence how to do the problem, just the question and needed numbers.

Sorry, it won't work this way. You will either show your work so that we can check it, or you will not get any help. That's a forum policy.

[UG]

Come on mate! If you're confident of your answer, post it! 

[azzarn]

Alright sorry all, this is how I thought to do it.
First we need to find the energy of the phase change, where q=m*Change in H_VAP.
So: (100g/78g/mol)=1.28mol*30.8kJ/mol=39.42kJ. But the problem is, the equation calls for mass, but the constant in in moles/kJ. Here, I converted to moles.
Then: Q=M*C*Delta T so Q=100g*1.72j/g*C *55 degrees Celsius. so Q=9460J, or 9.46 kJ.
Using Hess's Law we can add those two numbers, yielding 48.9 kJ of energy.

That is how I thought to to it, but how we did it in class dealt with proportions. Does anyone see any problems in my work?

Thanks for looking!

[Borek]

48.9 kJ of energy.

Looks OK to me.

That is how I thought to to it, but how we did it in class dealt with proportions.

And you got different result? Can you show how it was done in the class?