Question
I'mconfused about a calculation. From Hess' law and the heats offormation, I calculated deltaH to be 142.07-2(107.32)=deltaH=-72.57 kJ -fromliterature values given This is way off fromthe experimental value, which I think is in Joules, but I thinkthat I'm only off by a decimal place. Furthurmore, I believemy error is in the way I entered my R value. Can you help meclairify this for a lab report? This is the data from the graph and how I calculated deltaHfrom the slope of the graph, which is 9240. What should I usefor R and what units? slope =-deltaH/R 9240 (from graph)= delta H / .0820574 detaH = 758.21 = .75821 kJ using a differentR 9240 = deltaH/.08314 deltaH = 768.257 =.768257 kJ Why am I so off? Do you know? I'm pretty sure it is my R value units, but Idon't know where I'm off I'mconfused about a calculation. From Hess' law and the heats offormation, I calculated deltaH to be 142.07-2(107.32)=deltaH=-72.57 kJ -fromliterature values given This is way off fromthe experimental value, which I think is in Joules, but I thinkthat I'm only off by a decimal place. Furthurmore, I believemy error is in the way I entered my R value. Can you help meclairify this for a lab report? This is the data from the graph and how I calculated deltaHfrom the slope of the graph, which is 9240. What should I usefor R and what units? This is the data from the graph and how I calculated deltaHfrom the slope of the graph, which is 9240. What should I usefor R and what units? slope =-deltaH/R 9240 (from graph)= delta H / .0820574 detaH = 758.21 = .75821 kJ using a differentR 9240 = deltaH/.08314 deltaH = 768.257 =.768257 kJ Why am I so off? Do you know? I'm pretty sure it is my R value units, but Idon't know where I'm off
Explanation / Answer
The problem is that you are using and R that has the wrongunits. The first R you are using has the Units ofLatmK1mol1 the second R that you use has the units ofLbarK1mol1 Both of which don't have any unit of Joules. the correct Rthat you should use is this. 8.314472JK1mol1. This has the same numbers as your second value but in the correctunits to give you a fingue that is a lot close to the literaturevalue you calculated. the second R that you use has the units ofLbarK1mol1 Both of which don't have any unit of Joules. the correct Rthat you should use is this. 8.314472JK1mol1. This has the same numbers as your second value but in the correctunits to give you a fingue that is a lot close to the literaturevalue you calculated.