Unit 2 – Energy Transfer!

• Energy: the capacity to do work (the ability to move or change matter); energy has no mass and no volume; it’s intangible; it’s NOT matter.

Three types of energy we talk about• Kinetic: energy of motion• Potential: energy due to position; chemical potential

energy is energy stored in bonds and Intermolecular Forces

• Radiant/Electromagnetic energy (heat and light) we are mostly concerned with heat

Heat versus TemperatureHeat

• Def: energy due to molecular motion• Symbol = Q• Units: joules (j) or calories (cal)• Measured only when it is used to do work• Does work by speeding up the motion of

molecules and atoms• Flows from hot areas to cold areas• Heat is dependent on mass (the more stuff there

is, the more energy it can have overall)

Heat versus TemperatureTemperature

• Def: a measure of the average Kinetic Energy (KE) of a substance

• Symbol = T• Units: Kelvin (K) or degrees Celsius (°C)• Refers to the intensity of heat in an object• Change in T = ΔT = Tf - Ti

• Temperature is NOT a form of energy• Temperature IS a predictor of heat flow from areas of

high T to low T• Objects can be the same temperature but have

different amounts of heat energy

Temperature Scales

• Sig figs and temperature: because the Celsius temperature scale is a continuum with both positive and negative values, a temperature measurement of 0°C has 1 sig fig (0.1°C = 2 sig figs; 0.98°C = 3 sig figs)

• 0 K absolute zero; all molecular motion stops (all atoms condense into one big fuzzy atom)

• 0 K theoretical temperature not yet obtained (within a millionth of a degree)

Conversions

K = °C + 273

°C = K – 273

°F = (9/5*°C) + 32

°C = 5/9* (°F – 32)

These two will be

the most important

Some temperatures you should know off the top of your head…

What is happening °C K °F

Water melts/freezes 0 273 32

Water boils/condenses 100 373 212

Try a few!

• 450 K First to CelsiusEquation: °C = K – 273Calculations: °C = 450 – 273 = 177 °C

Then to FahrenheitEquation: °F = (9/5*°C) + 32Calculations: °F = (9/5 * 177 °C ) + 32 = 318.6 + 32 =

350.6 °F = 351 °F with sig figs

Try a few!

• 98.6 °F First to CelsiusEquation: °C = 5/9* (°F – 32)Calculations: °C = 5/9* (98.6 – 32) = 5/9*66.6 = 37°C

Then to KelvinEquation: K = °C + 273Calculations: K = 37 °C + 273 = 310 K

Work together

• Spend about 5 minutes practicing some of the others on the bottom of p.1 of your notes

Kinetic Molecular Theory *

1. Matter is made up of tiny particles (atoms, molecules)

2. The particles are in constant, random motion3. Collisions between particles are elastic (all

energy stays as motion, none is lost to heat)

*the basic principles of KMT are theoretical and begin to break down under certain circumstances KMT is better at describing matter in high energy states (gases, for example)

States/Phases of matterState Shape &

volumeDistance between molecules

Entropy (disorder) Motion of particles

Solid Definite shape and volume

Small No disorder (particles stay in the same position relative to one another)

No random motion (fixed positions)

Liquid Indefinite shape and definite volume

Small Much disorder (particles move past each other but continue touching)

Some random motion (flowing)

Gas Indefinite shape, indefinite volume

Large Much disorder (particles move randomly, not touching, only sometimes colliding)

Completely random motion (diffusion)

Law of Conservation of Energy• within a closed system, energy transforms from

one type to another• energy is never created nor destroyed • example: electricity lights a bulb: resistance

builds up in the tungsten wire, it glows and gives off light and heat; the total energy in the heat and light = energy in the electricity

• example: when heat is added to water on a hot plate, that heat energy is absorbed by the water molecules, which move faster and faster (increased kinetic energy higher temperature)

Law of Conservation of Matter• matter can also be transformed during chemical and physical

changes• During these changes, matter is never created or destroyed.• example: when ice melts to make water during a phase change,

every molecule of H2O in the original ice crystal/cube can be accounted for in the resulting liquid H2O

• example: when two chemicals are mixed, the atoms may be rearranged to form new chemical compounds, but every original atom can be accounted for in the new substances

(on our large scale, we see matter and energy as separate, but matter and energy interconvert at the subatomic level according to Einstein’s Theory of Relativity E = mc2)