Homework Help: chemistry

Posted by seth on Saturday, August 15, 2009 at 10:17am.

In which one of the following processes is ΔH = ΔE?

a. 2HI(g) → H2(g) + I2(g) at atmospheric pressure.

b. Two moles of ammonia gas are cooled from 325°C to 300°C at 1.2 atm.

c. H2O(l) → H2O(g) at 100°C at atmospheric pressure.

d. CaCO3(s) → CaO(s) + CO2(g) at 800°C at atmospheric pressure.

e. CO2(s) → CO2(g) at atmospheric pressure.

chemistry - DrBob222, Saturday, August 15, 2009 at 2:30pm
Delta E = delta H -p*delta V
where work is p*delta v.
So if delta v is zero, then there is no work and delta E = delta H = q_p
Note that when a reaction is at constant P, then a change in moles will result in a change in volume.
For a)
H2 + I2 ==>2HI
The work is zero because p*delta V is zero (because there are two moles of gas on the left and two moles of gas on the right). No change in moles, no change in volume and delta v is zero.

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