Question

chem 303 - tuboul 5. sate & thermochemistry
individual quiz (20 minutes)
name:
quiz version:
(first and last)
ucid:
3
multiple-choice questions (auto - graded)
shade the bubbles corresponding to your answers completely and darkly.

1. which of these statements about pv work and enthalpy is/are correct? select all the

correct answers. a penalty will apply for any incorrect statement chosen. 3 points
a. a reaction with a negative \\( \delta h \\) has no activation energy (i.e. it does not require
energy input to begin reacting).
b. the value of \\( \delta h \\) for a reaction depends on the amount of work that is done to or by
c. the enthalpy of a reaction (in kj) will depend on the quantity of products made
d. a reaction with a positive value for enthalpy will take in energy from the
surroundings while the reaction proceeds.
e. work can be done both by and on the system simultaneously.
f. work is done on the system when the volume increases (against a constant external
g. work is done by the system when the volume increases (against a constant external
pressure)
short answer question (auto - graded)
answer each question with a word, expression, number or symbol in the box provided.

1. complete the sentence: 2 points

silver sulfate \\( \left(\mathrm{ag}_{2} \mathrm{so}_{4}\
ight) \\) is a sparingly soluble salt \\( \left(k_{s}=1.5 \times 10^{-1}\
ight) \\). the molar solubility of silver
sulfate in pure water is \\( \mathrm{mol} / \mathrm{l} \\).

Explanation:

Multiple-Choice Questions

a. $\Delta H$ (enthalpy change) is unrelated to activation energy; even exothermic reactions need activation energy.
b. $\Delta H$ is a state function, independent of work done/path.
c. Enthalpy is extensive, so it depends on product quantity.
d. Positive $\Delta H$ means endothermic (absorbs energy from surroundings).
e. Work can’t be done both on and by the system simultaneously.
f. Volume increase at constant pressure means system does work (not work done on it).
g. Volume increase at constant pressure: $w = -P\Delta V$, so work done by system.

Step1: Write dissociation equation

$Ag_2SO_4(s)
ightleftharpoons 2Ag^+(aq) + SO_4^{2-}(aq)$
Let molar solubility = $s$. Then $[Ag^+] = 2s$, $[SO_4^{2-}] = s$.

Step2: Set up $K_{sp}$ expression

$K_{sp} = [Ag^+]^2[SO_4^{2-}] = (2s)^2(s) = 4s^3$

Step3: Solve for $s$

$s^3 = \frac{K_{sp}}{4} = \frac{1.5 \times 10^{-5}}{4} = 3.75 \times 10^{-6}$
$s = \sqrt[3]{3.75 \times 10^{-6}} \approx 1.55 \times 10^{-2}$

Answer:

C. The enthalpy of a reaction (in kJ) will depend on the quantity of products made during the reaction., D. A reaction with a positive value for enthalpy will take in energy from the surroundings while the reaction proceeds., G. Work is done by the system when the volume increases (against a constant external pressure)

Short Answer Question