Download 9.1 Heat and Temperature

Unit 9: Thermodynamics
Content Outline: Heat and Temperature (9.1)
I.
Thermochemistry
A. A branch of chemistry that focuses on the transfers of energy as heat.
1. The transfer is a direct result of a chemical reaction or physical change, such ice going to water.
II. Heat
A. The energy transferred between matter (atoms, molecules, objects) is due to a difference in the
matter’s temperatures.
1. Heat is always transferred from the matter of higher temperature to the matter of lower
temperature spontaneously. Just like diffusion and osmosis.
a. This is referred to as thermodynamically favorable.
B. Heat is measured in Joules (J)
1. Named in honor of the English Physicist James Prescott Joule.
C. Heat is measured using a device called a calorimeter.
III. Temperature
A. A measurement expressing the average kinetic energy of the particles in a sample of matter (solid,
liquid, or gas).
1. As Kinetic Energy of molecules increases, so does the temperature of that sample of matter.
B. Temperature can be measured in Fahrenheit, Celsius, or in Kelvin.
1. K = 273 + OC
2. OC = (OF -32) x 5/9
3. OF = (9/5 x OC) +32
IV. Specific Heat (CP) A value of energy associated with that specific substance.
A. The amount of energy required to raise the temperature of a one gram sample of a substance by 1OC
or 1K.
B. The material (solid, metal, liquid, gas) is IMPORTANT!
1. Metals generally have very low specific heats (CP).
a. The atoms are very close together, so heat spreads quickly.
b. This is why metals make good cooking items, such as pots and pans.
2. Gases tend to have high specific heats.
a. The atoms are very far apart, so heat is not easily spread.
3. Water has an extremely high specific heat.
a. CP = 4.18 joules/(g*K)
b. It is so high due to the numerous Hydrogen bonds per molecule.
c. Remember, each molecule can make up to four Hydrogen bonds each. They are far enough
apart to keep heat from transferring easily. Plus all four have to “break” simultaneously to
allow water to evaporate to a gas.
C. Units expressed as: J/(g*K).
D. Mathematically calculated as:
CP = q
m x ΔT
1. CP = Specific Heat
2. m = mass of sample in grams
3. ΔT = difference in temperature measured in K or OC
4. Q = energy lost or gained by the sample
E. Possible other forms of the equation:
1. q = CP x m x ΔT
2. m = CP/q x ΔT
3. ΔT = CP/q x m
V. Calorie
A. The amount of energy required to raise 1 gram of water by 1OC.
a. Food calories are actually kilocalories, so 1 food calorie = 1,000 actual calories.
b. This is done to make people think they are not eating so much food. Would you eat a Big Mac if it
said 549,000 calories…probably not?