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 thermometer (Heat meter) Thermometer Thermometers are filled with a liquid (mercury) 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 • Fahrenheit • Celsius (centigrade) • Kelvin – 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 Temperatures 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! .