how to do this type of Chemistry problem ?

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If a system has 3.00x10^2 kcal of work done to it, and releases 5.00x10^2 KJ of heat into the surroundings, what is the change in internal energy of the system. what is the KJ ?

Oct 23rd, 2015

Thank you for the opportunity to help you with your question!

This is based on  first law of Thermodynamics which states :  

DU = q + w 

. In this case (the convention adopted by scientists),

 q is positive if heat flows into the system and  w is positive is the work is done on the system, 

3.00*10^2  kcal of work is done ON the system, so w is positive. Heat, however, flows FROM the system, so q is negative. 

To do the problem in In kJ: 

DU = -5.00*10^2 kJ + (3.00*10^2 kcal)*(4.184 J/cal)

 = - 500 Kj + 1255.2 KJ = + 755.2 kJ (answer) 

Please let me know if you need any clarification. I'm always happy to answer your questions.
Oct 23rd, 2015

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