Transcript Section 2.3 Day 2

Friday, Oct. 4th: “A” Day
Monday, Oct. 7th: “B” Day
Agenda
Homework Questions/Collect
Finish 2.3: “Measurements and Calculations in
Chemistry”
Specific heat, scientific notation
Homework:
Pg. 63: #1-8, 10, 11
“Scientific Notation/Significant Figures” WS
Concept review: “Measurements and
Calculations in Chemistry”
Homework Questions
“Significant Figures Practice” worksheet
“Additional Problems” worksheet
Problems/Questions?
Hand In
Specific Heat
Remember, specific heat is the amount of
energy that must be transferred as heat to
raise the temperature of 1 g of a substance
by 1K or 1°C.
The amount of energy depends on:
The nature of the material
The mass of the material
The size of the temperature change
Calculating Specific Heat
 The specific heat of a substance at a given
pressure is calculated by the formula:
Cp =
q_____
(m) (ΔT)
Cp is the specific heat at a given pressure
q is the energy transferred as heat (Joules)
m is the mass of the substance (grams)
ΔT if the difference between the initial and
final temperatures (K)
Sample Problem B, pg. 61
A 4.0 g sample of glass was heated from 274 K
to 314 K and was found to absorb 32 J of
energy as heat. Calculate the specific heat of
this glass.
Cp =
q_____
(m) (ΔT)
q = 32 J
m = 4.0 g
ΔT = 314K – 274K = 40 K
0.20 J/g•K (2 sig figs)
Practice #1, pg. 61
Calculate the specific heat of a substance if a
35 g sample absorbs 48 J as the temperature
is raised from 293 K to 313 K.
Cp =
q_____
(m) (ΔT)
q = 48 J
m = 35 g
ΔT = 313K – 293K = 20 K
0.069 J/g•K (2 sig figs)
Scientific Notation
Chemists often make measurements and
perform calculations using very large or very
small numbers.
To make calculations with these numbers easier,
scientists use scientific notation.
In scientific notation, the exponent on the
number 10 tells how many places the decimal
point moves.
To change a number into scientific notation,
follow these steps:
1. Put a decimal point after the first non-zero digit.
2. Add a multiplication sign and then the number 10.
3. Count how many spaces the decimal point moved
and make that the exponent on the number 10.
4. If the original number was less than 1, the sign on
the exponent is negative!
5. If the original number was more than 1, the sign
on the exponent is positive!
Scientific Notation Examples
Write the following in scientific notation:
1. 123,000 grams
1.23 X 105 grams
2. 9,125,600 liters
9.1256 X 106 liters
3. 0.000931 meters
9.31 X 10-4 meters
Scientific Notation with Sig Figs
 Scientific notation eliminates non-significant
zeros.
2,400 meters
2.4 X 103 meters
(the two 0’s are NOT significant)
 When doing calculations, the answer must
contain the correct # of sig figs.
 5.44 X 107 = 671.6049383
8.1 X 104
6.7 X 102
(2 sig figs)
Homework
Sec. 2.3 review, pg. 63: #1-8, 10, 11
“Scientific Notation/Significant Figures”
Worksheet
PAPERS DUE NEXT TIME!!
Concept Review: “Measurements and
Calculations in Chemistry”
Next time: Quiz over sec. 2.3
Ch. 2 test/concept review due:
“A” Day: Thurs. 10-17
“B” Day: Fri. 10-18