Dear students of the class of
physical-chemical processes, I share some problems and exercises for you to
solve.
Bring them next Monday
best regards
Problems
1. Which of the
following is a chemical reaction?
- Freezing
liquid Mercury
- Adding yellow to blue to make green
- Cutting a piece of paper into two pieces
- Dropping a sliced orange into a vat of Sodium
Hydroxide
- Filling a balloon with natural air
2. Which of the
following is a physical reaction?
- Shattering
Glass with a baseball
- Corroding
Metal
- Fireworks
Exploding
- Lighting
a match
- Baking
a cake
3. Which of the
following is a chemical reaction?
- Painting
a wall blue
- A
bicycle rusting
- Ice
cream melting
- Scratching a key across a desk
- Making
a sand castle
4. Which of the
following is a physical reaction?
- Frying
an egg
- Digesting
carrots
- A Macbook falling out of a window
- Creating ATP in the human body
- Dropping a fizzy tablet into a glass of water
5. Write C for
Chemical Reaction or P for Physical Reaction.
- Burning
Leaves
- Cutting
Diamonds
- Crushing
a pencil
- The salivary amylase enzyme that breaks down food
in the mouth
- Salt
mixing in with water
Exercises
1.- Guevara has just installed solar collectors to
heat water. His large water tank holds 400 liters of water. The solar
collectors have an area of 8 m2 (2 meters by 3 meters). If the water in his
tank starts out with a temperature of 20◦C in the morning, what is its temperature
in the evening after the sun has set? Some useful information: solar energy
intensity is around 800 W/m2 , solar collectors have an efficiency of around
30%, and suppose the sun shines for 8 hrs/day.
2.- One mole of an ideal, monatomic gas runs through a
four step cycle. All processes are either isobaric or isochoric. The pressure
and volume of the gas at the extreme points in the cycle are given in the first
two data rows of the table below.
a.
Sketch
the PV graph of this cycle.
b.
Determine
the temperature at state A, B, C, and D.
c.
Calculate W, Q,
and ΔU on the path A→B, B→C, C→D, D→A and for one
complete cycle. (Include the algebraic sign with each
value.)
d.
Does
this cycle behave more like an engine or a refrigerator?
|
A four step
cycle (isobaric & isochoric)
|
|
state
|
A
|
B
|
C
|
D
|
|
|
P
|
(Pa)
|
100,000
|
200,000
|
200,000
|
100,000
|
|
|
V
|
(m3)
|
0.020
|
0.020
|
0.060
|
0.060
|
|
|
T
|
(K)
|
|
|
path
|
A→B
|
B→C
|
C→D
|
D→A
|
ABCDA
|
|
description
|
isochoric
|
isobaric
|
isochoric
|
isobaric
|
closed cycle
|
|
ΔU
|
(J)
|
|
|
Q
|
(J)
|
|
|
W
|
(J)
|
|
