Midterm Review #12b

[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?

[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.

[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?

[Daria Azizad 1K]

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

[Jamie Wang 3C]

How do we calculate for this? because doesn't q1 and q3 cancel each other out?