physical-chemical processes, summer 2019

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?

1. Freezing liquid Mercury
2. Adding yellow to blue to make green
3. Cutting a piece of paper into two pieces
4. Dropping a sliced orange into a vat of Sodium Hydroxide
5. Filling a balloon with natural air

2. Which of the following is a physical reaction?

1. Shattering Glass with a baseball
2. Corroding Metal
3. Fireworks Exploding
4. Lighting a match
5. Baking a cake

3. Which of the following is a chemical reaction?

1. Painting a wall blue
2. A bicycle rusting
3. Ice cream melting
4. Scratching a key across a desk
5. Making a sand castle

4. Which of the following is a physical reaction?

1. Frying an egg
2. Digesting carrots
3. A Macbook falling out of a window
4. Creating ATP in the human body
5. Dropping a fizzy tablet into a glass of water

5. Write C for Chemical Reaction or P for Physical Reaction.

1. Burning Leaves
2. Cutting Diamonds
3. Crushing a pencil
4. The salivary amylase enzyme that breaks down food in the mouth
5. 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)