Summary Practice

NAME:___________________________ Section:_____ Student Number:__________________

Spring 2020 Chemistry 2000 Midterm #2A ____/ 65 marks

INSTRUCTIONS: 1) Please read over the test carefully before beginning. You should have 8 pages
of questions, a blank “overflow” page and two pages of data sheets with
periodic table.
2) If your work is not legible, it will be given a mark of zero.
3) Marks will be deducted for incorrect information added to an otherwise correct
answer.
4) Marks will be deducted for improper use of significant figures and for missing
or incorrect units.
5) Show your work for all calculations. Numerical answers without supporting
calculations will not be given full credit.
6) You may use a calculator but only for the purposes of calculation. No text-
capable calculators are allowed.
7) You have 90 minutes to complete this test.



Confidentiality Agreement:
I agree not to discuss (or in any other way divulge) the contents of this exam until after 8:30 pm Mountain
Time on Tuesday, March 17th, 2020. I understand that breaking this agreement would constitute academic
misconduct, a serious offense with serious consequences. The minimum punishment would be a mark of
0/65 on this exam and removal of the “overwrite midterm mark with final exam mark” option for my grade
in this course; the maximum punishment would include expulsion from this university.


Signature: ___________________________ Date: _____________________________
Course: CHEM 2000 (General Chemistry II)
Semester: Spring 2020
The University of Lethbridge


Question Breakdown
Q1 /7
Q2 /6
Q3 / 13
Q4 / 10
Q5 /3
Q6 /8
Q7 / 18

Total / 65

, NAME:___________________________ Section:_____ Student Number:__________________

1. [7 marks]
(a) Complete each statement with one of the following symbols: >, < or = [4 marks]
For an allowed process at constant temperature and pressure,
i. ∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 > 0
ii. ∆𝐺 < 0
iii. 𝐸 > 0
iv. 𝐾 > 𝑄
(b) One of the statements in part (a) is true under any conditions (not just at constant temperature and
pressure). Which one? [1 mark]
∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 > 0
(c) In statement (a) i., why do we have to write ∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 ? Why can’t we just write ∆𝑆? [1 mark]
∆𝑆 refers to the entropy change for the system only. ∆𝑆𝑢𝑛𝑖𝑣𝑒𝑟𝑠𝑒 also includes the entropy change
for the surroundings, and the second law of thermodynamics states that the entropy of the universe
must increase in any thermodynamically allowed process.
(d) In statement ii. in part (a), can ∆𝐺 be replaced by ∆𝐺°? Why or why not? [1 mark]
No.
∆𝐺° refers specifically to the free energy change of a reaction under standard conditions. ∆𝐺
refers to the free energy change of a reaction under whatever conditions it is actually being run.



2. Consider the following reaction that takes place in aqueous acid. [6 marks]
2− 2+ 3+
𝐶𝑟2 𝑂7(𝑎𝑞) + 𝑍𝑛(𝑠) → 𝑍𝑛(𝑎𝑞) + 𝐶𝑟(𝑎𝑞)
(a) Balance this equation under acidic conditions. [3 marks]
For full marks, your answer must include balanced half reactions.
2+
( 𝑍𝑛(𝑠) → 𝑍𝑛(𝑎𝑞) + 2 𝑒− ) × 3
2− + 3+
𝐶𝑟2 𝑂7(𝑎𝑞) + 14 𝐻(𝑎𝑞) + 6 𝑒 − → 2 𝐶𝑟(𝑎𝑞) + 7 𝐻2 𝑂(𝑙)
2− + 3+ 2+
𝐶𝑟2 𝑂7(𝑎𝑞) + 3 𝑍𝑛(𝑠) + 14 𝐻(𝑎𝑞) → 2 𝐶𝑟(𝑎𝑞) + 3 𝑍𝑛(𝑎𝑞) + 7 𝐻2 𝑂(𝑙)
(b) Identify the oxidizing agent. [1 mark]
𝐶𝑟2 𝑂72−
(c) Identify the reducing agent. [1 mark]
𝑍𝑛
(d) What is 𝜈𝑒 for this reaction? [1 mark]
6