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Midterm Review #12b

Posted: Sun Feb 09, 2020 11:08 pm
by Brian Tangsombatvisit 1C
Suppose a researcher finds that delta Hrxn = -2756 kJ for the reaction at 200. C. Assuming all heat capacities are constant, calculate delta Hrxn at the temperature of the human body, 37 C. Hint: since enthalpy is a state function, the process can be divided into three steps.

Can somebody help me on how to start this problem? What are the three steps we can divide this process into?

Re: Midterm Review #12b

Posted: Sun Feb 09, 2020 11:20 pm
by Kaitlyn Ang 1J
For this problem, you have 3 mini reactions. The first is the rise in temperature of the reactants. The second is the change from reactants to products at the higher temperature. The third is the decrease in temperature of the products.
In other words, the three steps are

1) the enthalpy change of the reactants from 37C to 200C
2) the enthalpy change of the reactants to products at 200C (this is given to you by the fact that the reaction is -2756 kJ)
3) the enthalpy change of the products from 200C back down to 37C

You would calculate steps 1 and 3 with the equation of deltaH = nCdeltaT and use the corresponding C to the specific reactant/product.

Re: Midterm Review #12b

Posted: Sun Feb 09, 2020 11:59 pm
by Brian Tangsombatvisit 1C
would the enthalpies for the reactants and products in steps 1 and 3 be both positive? or would reactants be positive and products be negative?

Re: Midterm Review #12b

Posted: Mon Feb 10, 2020 12:31 am
by Daria Azizad 1K
Brian Tangsombatvisit 1C wrote:would the enthalpies for the reactants and products in steps 1 and 3 be both positive? or would reactants be positive and products be negative?

if the calculation for q in step 1 is positive because final temp is higher than initial and in step 3 it is negative because final temp is lower than initial