Chemistry A Pre-Test
D= m
Heat transferred = mass x change in temp x specific heat capacity
V
Heat transferred = mass x Latent Heat
Physical Properties
11. Given the following data determine the density of the metal. Please show your work.
Round off the density to the correct number of significant figures. All of the units
should be included throughout your calculations.
D=m =
( 28.10 g)
= 7.805 g/ml = 7.81g/ml
(18.6 ml – 15.0 ml)
D=
( 40.00 g) = 7.018 g/ml =7.02 g / ml
( 20.7 ml – 15.0ml)
Avg D = 7.41 g/mL
The following data collected by liquid displacement can be used to determine the density of a metal
mass of a metal
= 28.10 g
volume of water in the cylinder
= 15.0 ml
Volume of the water in the cylinder + the metal
= 18.6 ml
Total mass of metal placed in the cylinder
= 40.00 g
Volume of the water in the cylinder + the metal
= 20.7 mL
12. a) What is the mass of 4.00 cm3 of aluminium? Al density is 2.7 g / cm3
Please show your work. Round off the density to the correct number of significant figures.
All of the units should be included throughout your calculations.
D=m
V
m= D V = 2.7 g / cm3 ( 4.0 cm3) = 10.8 g = 11 g
b) The density of Zinc is 7.1 g / cm3. Compare the volume of 4.00 g of zinc to 4.00 g of
aluminium.
The volume of the 4.00g of aluminium will be approximately 7.1/2.7 times
( 2.6 ) greater than the 4.00g of zinc. The volume of equivalent masses of matter is always
greater for the least dense sample of mater.
Significant figures
How many significant figures are in each of the following. If the number should be written in
scientific notation in order to determine the number of significant figures please state that. 1pt each
13. 6021 km
4
14. 170,800 km
sci notation
15.
.489m
3
16.
.00087 m
2
17. 4.070 g
4
18. Write that number that should be written in scientific notation to 5 significant figures in scientific
notation?
1.7080 x 105 km 2pts
Round off the following two calculations two the correct number of significant figures? 1pt each
19.
20.
m / D = V = 834.5 g / 1.26
g
= 662. 3 ml = 662 ml ( Least # of digits)
---ml
8 g + 5.036 g + 9.811 g = 22.847 g = 23 g ( Least # of decimal places )
Temperature, Specific Heat Capacity, Melting Pts, Boiling Pts, Heat of Fusion, Heat of
Vaporization, Phase Changes, Potential Energy Changes, Kinetic energy changes
21.
The following data can be used to predict the shape of a heating curve
Specific heat capacity of the solid = .25 cal / g oC
Specific heat capacity of the liquid = .50 cal / g o C
Specific heat capacity of the vapor = .125 cal / g oC
Heat of Fusion = 50 cal / g
Heat of Vaporization = 150 cal / g
The melting point of the substance is – 40 C
The boiling point of the substance is 20 C
The substance starts out at – 60 C
The substance ends at + 80 C
Sketch the curve
Indicate on the graph changes in kinetic energy and changes in potential energy
Temperature as a function of
time heating 10g of a substance
at a rate of 5cal/s
100
80
60
temperature oC
40
20
0
-20 0
100
200
300
400
-40
-60
-80
time heating in seconds
500
-60oC to -40oC Q=mct
time = Q
rate
Q=10g(-40oC-(-60OC))(.25cal/goC)=50cal
50 cal = 10s
5 cal /s
-40 oC to -40 oC
Q=mLf time = Q
rate
Q = 10g ( 50 cal /g ) =500 cal
500 cal = 100s
5 cal/s
-40oC to 20oC Q=mct
time = Q
rate
Q=10g(20oC-(-40OC))(.50cal/goC)=75cal
300 cal = 60s
5 cal /s
20 oC to 20oC
Q=mLf time = Q
rate
Q = 10g ( 150 cal /g )= 1500 cal
1500 cal = 300s
5 cal/s
20 oC to 80 oC Q=mct
time = Q
rate
Q=10g(80oC-20OC))(.125cal/goC)=75cal
75 cal = 15s
5 cal /s
22. If you touch a sample at -25 C describe the heat transfer between the sample and your
finger? What direction is the heat transfer and why?
Since your finger is above -25 oC than heat will be transferred from your finger to the
sample. Heat flows from a higher temp sample to a lower temp sample.
23. Heat Absorbed Heat Released
a) Given the following information which reaction releases the most energy to the
Water and why ? Reaction 1 because the water warmed had the greatest mass and greatest
temperature change _____________________________________________________
Reaction 1
Reaction 2
Reaction 3
Reaction 4
Reaction 5
mass of water initial temperature
of the water
g
C
30.0
(20
20.0
(25
30.0
(20
20.0
(25
30.0
(20
final temperature
of the water
C
50) ( 1cal/g oC) = -900 cal
40) ( 1cal/g oC) = -300 cal
30) ( 1cal/g oC) = -300 cal
20) ( 1cal/g oC) = +100 cal
10) ( 1cal/g oC) = +300 cal
b) Calculate the number of calories involved in reaction 5.
specific heat capacity of water = 1 cal / goC
Q = 30.0g (20oC -10oC) ( 1cal/g oC) = +300 cal = 3 x102 cal
24. Heat is added to a solid at its melting point of 200 C at a rate of 4000 J per minute. It
takes 3.00 minutes to melt 11 grams of the solid. What is the heat of fusion of the solid at
200 C in J per Kilogram. (1000g = 1kg)
Q = 4000 J / min ( 3.00 min ) = 12,000 J to melt the solid
Q = 12,000 J = 1090 J
11 g
g
( 1000 g ) = 1.09 x10 6 J
( Kg )
kg
25. The specific heat capacity of aluminum is .88
The specific heat capacity of lithium is
Joules
----------g C
2.78 Joules
----------g C
If 500 calories of heat were absorbed by the 20.00 g of lithium and 20.00 g aluminium which would
at 20 oC which sample would have the highest temperature and why?
The aluminium will experience the greatest change in temperature because it requires the least
amount of energy ( .88 J / g C) to change its temperature compared to the lithium with its higher
specific heat capacity (2.78 J / g C)
26. What is the difference between the measurement of temperature and the calculation of heat?
How are they related?
One way to measure temperature of a sample is to measure the height of a liquid in a glass
tube relative to known standards such as the freezing point of water and the “normal”
boiling. Temperature is a measure of how warm or cool a sample is relative to these known
standards. On an atomic level two samples that are at the same temperature contain
particles with same average kinetic energy.
The heat absorbed or released by a sample is determined by multiplying the mass of the
sample by its temperature change by the amount of energy required to raise the temperature
of 1 kilogram 1 degrees Celsius. Scientist have chosen to measure heat transfer in reference
to temperature changes, however the temperature change alone cannot tell you the amount
of heat transferred.
The heat absorbed or released by a sample can also be determined if there is no temperature
change. The heat absorbed or released during a phase change can be calculated by
knowning the mass of the sample multiplied by the Latent heat of fusion or Latent heat of
vaporization.
27.
What is the difference between the specific heat capacity of a liquid and the latent heat of
of vaporization liquid?
The specific heat capacity of a substance is calculated by determining the amount of energy
required to raise the temperature of 1 kilogram 1 degrees Celsius.
The latent heat of vaporization involves no temperature change.
The latent heat of vaporization is calculated by determining the amount of energy per
kilogram to vaporize 1 kg of the liquid at its boiling point.
Why is it important that it takes 2.24x106 J / kg to vaporize water to life on this planet?
It is important that it takes a very large quantity of energy to vaporize water because it
allows most of the water in this planet to stay in the liquid phase at the range of temperatures found
on this planet. If it were less than there most likely would be more precipitation and drastic
changes in climates.
28.