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Ekayana Sethi 2K
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Postby Ekayana Sethi 2K » Thu Jan 25, 2018 5:40 pm

the enthalpy of vaporization is deltaH=Hvapor-Hliquid. What is the difference between deltaH and just H and where do we find the values for H(NOT deltaH!) of vapor or liquid of a substance?

Deborah Cheng 1F
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Joined: Thu Jul 13, 2017 3:00 am

Re: enthaply

Postby Deborah Cheng 1F » Thu Jan 25, 2018 6:10 pm

Delta refers to the difference or change in a quantity. In this case, deltaH is the difference in the enthalpies of vapor and liquid. It seems that so far in this chapter we're given deltaH of vaporization/fusion and we're asked to do calculations from there using those values. For the homework problems I just used Table 8.3 on page 284 when the problems required deltaH of fusion and vaporization.

Helen Shi 1J
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Joined: Sat Jul 22, 2017 3:00 am

Re: enthaply

Postby Helen Shi 1J » Thu Jan 25, 2018 6:22 pm

H is simply enthalpy whereas delta H is the change in enthalpy. Enthalpy itself is the total heat content (energy) of a system: aka the internal energy plus the product of pressure and volume. My guess as to why we use the change in enthalpy is because it is easier to calculate through experiments.

Angela 1K
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Joined: Fri Sep 29, 2017 7:05 am

Re: enthaply

Postby Angela 1K » Thu Jan 25, 2018 9:10 pm

You can't necessarily measure just the enthalpy (H) of a system. Rather, when we calculate the heat that is transferred during an equation, we want to compare the heat before and after the reaction has occurred, thus we would always use in terms of measuring the enthalpy change.

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