Calculations in Chemistry Scientific Math. Over the next few lessons you will learn some basic math essential to studying chemistry: – Temperature Scales/Conversions.

Calculations in Chemistry

Scientific Math

• Over the next few lessons you will learn some basic math essential to studying chemistry:– Temperature Scales/Conversions– Scientific Notation– Significant Figures in Measurement/Calculations

• I CAN convert between common and scientific temperature scales.

Temperature vs Heat

• What is TEMPERATURE and how is it different from HEAT?

• Temperature and Heat are NOT the same thing.• How are they different? Remember KINETIC ENERGY?• HEAT is a measure of the TOTAL ENERGY possessed by

a substance.• TEMPERATURE is a measure of the AVERAGE ENERGY

possessed by the particle of a substance.

Example• Two beakers of water are placed on a hot plate

and heated until both reach the boiling point of water, 100 °C.

• What is the TEMPERATURE of each beaker?• 100 °C• Which beaker of water has MORE ENERGY?• The larger one on the right.

Temperature Scales• Since the invention of the first modern

thermometer in 1724, scientists have created a number of temperature scales.

• A common widely used scale is the FAHRENHEIT scale.

• Freezing Point (water) 32 oF.• Boiling Point (water) 212 oF.• 180 degree range between FP and BP.• Temperatures can be LESS THAN ZERO.

CELSIUS TEMPERATURE SCALE

• The Celsius Scale is the preferred scale for most scientific work.

• Part of the SI (Metric) System• Freezing Point is 0 oC.• Boiling Point is 100 oC.• 100 degree range between FP and BP.• Temperatures can be LESS THAN ZERO.

• For most science work the Celsius Scale is fine. However, in some calculation, temperatures less than ZERO present a problem.– Example Volume/Mass calculations cannot use

temperatures less than zero because volume or masses CANNOT BE NEGATIVE.

• In these instances, a third scale is used.

• The KELVIN SCALE is based on the expansion and contraction of matter.

• For every degree of change (+ or -) Kelvin, matter expands or contracts by 1/273.15 of its original volume.

• If matter’s temperature could be lowered to -273.15 K, matter would have a ZERO VOLUME, which is THEORETICALLY impossible.

• This temperature is known as ABSOLUTE ZERO.

• At this temperature matter would possess NO KINETIC ENERGY!

• Scientist have come within a few millionths of a degree of absolute zero!

Temperature Calculations

• Often in scientific work, it is necessary to convert temperatures from one system to another.

• This is easily done with the appropriate equation.

Fahrenheit to Celsius

• To convert a temperature given in oF to Celsius, use this equation:

• oC = 0.56(oF-32)

Celsius to Fahrenheit

• To convert a temperature in oC to Fahrenheit, use this equation:

• oF = 1.8 (oC) + 32

Converting Celsius Kelvin

• K = oC + 273.15

• oC = K – 273.15

• (Generally just 273 is fine!)

Fahrenheit Kelvin

• To convert Fahrenheit to Kelvin:

K = 0.56 (oF-32) + 273.15

Practice Problems

• Complete the practice problems sheet.

• I CAN convert number to and from SCIENTIFIC NOTATION.

What are Measurements

• A measurement is a QUANTITY with both a NUMBER and a UNIT.– In science, you will encounter very, very large

numbers as well as very, very small ones.– To simply the handling of such numbers, we often

write them in a compressed form called SCIENTIFIC NOTATION.

• In scientific notation, numbers with many digits are often written as a coefficient and a power of 10.

• Example 6.022 x 1023

• Coefficient

• Power of 10

Converting Numbers to Scientific Notation

• Converting numbers to scientific notation is easy.– 1. Locate the DECIMAL [may be an understood decimal]– 2. MOVE the decimal to the LEFT or to the RIGHT

until it is to the RIGHT OF THE FIRSTNON-ZERO DIGIT in the number.

– Example 24567.88 would be 2.456788

– 3. COUNT THE NUMBER OF PLACES the decimal was moved…this is the POWER OF 10.

• When the decimal is moved to the LEFT the power of 10 is POSITIVE.

• When the decimal is moved to the RIGHT the power of 10 is NEGATIVE.

• You may DROP TERMINAL ZEROS to round off or follow the directions in the problem.

SAMPLE PROBLEM

• Convert this number to scientific notation:• 602200000000000000000000

1. Locate the decimal.2. Decide if the decimal needs to move left or right.3. Count the number of places it has to move.4. Rewrite the number with the decimal in its new location

[drop terminal zeros].5. Add the power of 10 with the correct sign.

• 602200000000000000000000

– Since there was no written decimal it is understood to be at the end of the number.

– Which direction should it be moved?• We will need to move it toward the LEFT to get it

between the first two non-zero digits.

• 602200000000000000000000

• The decimal was moved a total of 23 places to the left.

• 6 02200000000000000000000

• Drop the terminal zeros to get

• 6 022

• Since the decimal moved 23 places to the LEFT, the power of 10 is POSITIVE 23.

• So the number in scientific notation is:

6.022 X 1023

• MORE PRACTICE• Write this number is Scientific Notation:

• 0.0000475000

• 0.0000475000• Decimal First two non-zero digits

• This time the decimal has to be moved to the RIGHT. This will make

the power of 10 NEGATIVE.

• 000004.75000 • • DROP these zeros!

• 4.75

• The decimal was moved 5 places to the right, so the power of 10 is -5.

• 4.75 X 10-5

Write each number in scientific notation.

0.07882 =0.00000272338 =118000 =87200 =0.00002786 =0.000000664 =450 =74171.7 =770 =0.0000085 =

0.07882 = 7.882 × 10-2

0.00000272338 = 2.72338 × 10-6

118000 = 1.18 × 105

87200 = 8.72 × 104

0.00002786 = 2.786 × 10-5

0.000000664 = 6.64 × 10-7

450 = 4.5 × 102

74171.7 = 7.41717 × 104

770 = 7.7 × 102

0.0000085 = 8.5 × 10-6