How much heat is absorbed?

Question

When 1 mole of CS2 (l) forms from its elements at 1 ATM and 25 degrees C, 89.7 KJ is absorbed, and it takes 27.7 kJ to vaporize 1 mole of the liquid. How much heat is absorbed when 1 mole do CS2 (g) forms from its elements at these conditions?

Answer 1

Hi Diana!

 

Since enthalpy is a state function, we can determine the answer by breaking the process down into 2 steps.

 

The first step can be expressed as:

 

     C_(gr) + 2S_(s) ----> CS_{2 (l)}     delta H = +89.7 KJ/mole  (positive since heat is absorbed)

 

 

The second step can be expressed as:

 

     CS_{2 (l)} -----> CS_{2 (g)}           delta H = + 27.7 kJ/mole  (again positive since heat is absorbed to go from liquid to gas)

 

 

Adding these two equation together yields the desire result.

 

C_(gr) + 2S_(s)---> CS_{2 (g)}  delta H = +89.7 +27.7 = +117.4 KJ/mole 

 

Hope this helps!