LHSE Presents Introduction to Chemistry

Temperature Conversions

Previous lecture • Math for Chemistry

Temperature

• Heat

• Temperature

• 3 Temperature scales (Fo, Co, K)

• Equations for converting between scale

• Algebra with conversion equations

• Examples Heat The components of matter (atoms and compounds) are in constant motion – This includes those in solid objects.

Motion is energy Motion energy is Heat More motion means more Heat

Most substance expand with more motion (Heat)

Temperature Temperature is NOT: Motion Heat

Temperature IS: – a MEASUREMENT of the amount of Heat – Often measured using a (Heat meter) Thermometer are filled with a liquid () that expands when heated

Thermometers have a scale (to gauge the height of the liquid)

The scale is divided into equal parts, called degrees (°) – There are 3 common scales • • (centigrade) • – They measure the same height but give different numerical values • Like a ruler in inches and centimeters

Temperature scales Fahrenheit, an older scale (1724) in which water freezes at 32 °F and boils at 212 °F • Mainly used in the US; Scale HAS negative numbers Celsius is the modern scale in which water freezes at 0°C and boils at 100°C • There are 100 ° between the temperature of freezing & boiling (that is how the scale was constructed) • Scale HAS negative numbers

Kelvin is the absolute scale of temperature. • The lowest possible temperature is 0 K (no° sign) • Water freezes at 273.15 K and boils at 373.15 K • There are 100 ° between the temperature of freezing & boiling • Scale HAS NO negative numbers Same height Fahrenheit Celsius Kelvin different 71.5 Fo 22 Co 295.15K number of steps

-32 Fo 0 Co 273.15K

Same height different degrees

Formulas for Converting

Since each scale is reading the same temperature converting between scales doesn’t alter the true value for the “amount of heat”

Convert Fahrenheit Celsius = 5/9 * (Fahrenheit – 32) to Celsius Convert Celsius to Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit Convert Celsius to Kelvin = Celsius + 273.15 Kelvin Celsius = Kelvin - 273.15

Examples

Convert Fahrenheit Celsius = 5/9 * (Fahrenheit – 32) to Celsius

The average temperature of the human body is 98.6 oF. What is it in Celsius?

Celsius = 5/9 * (Fahrenheit – 32) Celsius = 5/9 * (98.6 – 32) Celsius = 5/9 * (66.6) = (5*66.6) /9 Celsius = 333/9 Celsius = 37 oC

Convert Celsius to Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit

When the thermometer reads 40 oC. What is the temperature in Fahrenheit ?

Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit = 9/5 * (40) + 32 = (9* 40) /5 + 32 Fahrenheit = (360) /5 + 32 Fahrenheit = 72 + 32 Fahrenheit = 104 oF Convert Celsius to Kelvin = Celsius + 273.15 Kelvin

Dry ice turns to gas at -78.5 oC. What is the temperature in Kelvin?

Kelvin = Celsius + 273.1 Kelvin = -78.5 + 273.1 Kelvin = 194.6 K

Convert Celsius to Kelvin = Celsius + 273.15 Kelvin

A balloon rising in the sky cooled the helium within to 281 Kelvin? What is it in Celsius?

Kelvin = Celsius + 273 - 273 -273 Kelvin -273 = Celsius 281 -273 = Celsius 8 = Celsius Algebra and Conversion Formula

Solve for Celsius

9 C + 32 = F Remove 5 − 32 − 32 the 32 5 9 ( C ) = 5 ( F − 32 ) Remove 9 5 9 the 9/5

5 C = ( F − 32 ) 9

Solve for Fahrenheit 5 9 C = 9 ( F − 32 ) Remove 5 9 5 the 5/9

9 C = ( F − 32 ) Remove 5 the -32 + 32 + 32

9 C +32 = F 5 Examples II The instruction on a pizza box says to bake at 425°F. What temperature is needed on the Celsius scale? What about on the Kelvin scale?

Convert Fahrenheit Celsius = 5/9 * (Fahrenheit – 32) to Celsius

Celsius = 5/9 * (Fahrenheit – 32) Celsius = 5/9 * (425 – 32) Celsius = 5/9 * (393) = (5*393) /9 Celsius = 1965/9 Celsius = 218.3oC

Examples II The instruction on a pizza box says to bake at 425°F. What temperature is needed on the Celsius scale? What about on the Kelvin scale? Convert Celsius to Kelvin = Celsius + 273.15 Kelvin

Convert Fahrenheit Celsius = 5/9 * (Fahrenheit – 32) to Celsius Celsius = 218.3oC

Kelvin = Celsius + 273.1 Kelvin = 218.3 + 273.1 Kelvin = 491.4 K Examples II The temperature on the moon can get to 400 Kelvin. What is the same temperature on the Celsius scale? What about on the Fahrenheit scale?

Convert Celsius to Kelvin = Celsius + 273.15 Kelvin

Kelvin = Celsius + 273 Kelvin -273 = Celsius 400 -273 = Celsius 123 oC = Celsius

Examples II The temperature on the moon can get to 400 Kelvin. What is the same temperature on the Celsius scale? What about on the Fahrenheit scale?

Convert Celsius to Kelvin Kelvin = Celsius + 273.15

Convert Celsius to Fahrenheit Fahrenheit = 9/5 * (Celsius) + 32

123 oC = Celsius Fahrenheit = 9/5 * (Celsius) + 32 Fahrenheit = 9/5 * (123) + 32 = (9* 123) /5 + 32 Fahrenheit = (1107) /5 + 32 Fahrenheit = 221.4 + 32 Fahrenheit = 253.4 oF RECAP • Atoms and compounds are in constant motion • Motion energy is Heat (atomic scale) • Temperature IS a MEASUREMENT of the amount of Heat • Thermometers have a scale (to gauge the height of the liquid) • There are 3 common scales Fahrenheit (water freezes at 32°F and boils at 212°F) Celsius (water freezes at 0°C and boils at 100°C) Kelvin (The lowest possible temperature is 0 K (no° sign)) • They measure the same height /different numerical values • There are Formulas for Converting between Temperatures scales Fahrenheit = 9/5 * (Celsius) + 32 Celsius = 5/9 * (Fahrenheit – 32) Kelvin = Celsius + 273.15

Practice!