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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: disillusioned19 on February 27, 2012, 08:36:13 AM

Title: Enthalpy change and expansion work
Post by: disillusioned19 on February 27, 2012, 08:36:13 AM

If we have an exothermic reaction ( i.e. ΔH = -ve) , using the equation ΔH = ΔU + P(external)ΔV, am I right in thinking that if ΔH is to be negative, ΔU will also be negative since the thermal energy of the molecules will decrease due to transfer of energy with the surroundings? If this is correct, what does this mean for the volume of the system in this case, does it increase or decrease, or stay the same?

Thanks in advance.

Title: Re: Enthalpy change and expansion work
Post by: Enthalpy on March 02, 2012, 11:37:48 AM

With a big volume change, especially a gas to of from a condensed state, you should get all the possible combinations of U and H positive and negative, wouldn't you?