Energy

Zumdahl 3.6 & 3.7

Energy is…

… “the ability to do work”…which means that only the effects of work (energy) can be measured.…whether that work is mechanical or

chemical or electrical or some other form….

Molecules involve chemical potential energy in the bonds AND heat energy in their motion

Temperature Average kinetic

energy of molecules of a sample

Measured in Fahrenheit, Celsius, Kelvin—based on freezing “temp” of water at 1atm.

F = 9/5C + 32 K = C + 273.15

Pause for demo…

I need two volunteers!!

;0)

Practice!! Convert the following temps:

37 ºC to Fahrenheit212 ºF to Celsius75 ºF to Kelvin

At what temperature would the Fahrenheit and Celsius read the same number?

How much hotter is 65ºF than 32ºF?

Heat Total amount of

energy of molecules of a sample

Measured in BTUs, calories, Joules Takes into account the

amount of sample AND the temperature of sample!

Defining units of Energy:

BTU—amount of energy required to raise 1 pound of water 1Fº

Calorie—amount of energy required to raise 1g of water 1Cº

Joule—energy required to move 1N object a distance of 1meter; named in honor of James Prescott Joule. 4.184J = 1 calorie (The mechanical definition had to

be converted to heat definition.)

Specific Heat

Amount of energy required to raise 1g of a certain material 1Cº.

Specific to each element/alloy Low specific heats = bad insulators

c = H/m·ΔT or H = mcΔT

More practice!

What quantity of energy is required to heat a piece of iron weighing 1.3g from 25ºC to 46ºC? (specific heat of iron = 0.45J/g·Cº)

Conservation of Energy: Energy cannot be created or destroyed—only converted

to another form Light/radiation Electrical Kinetic/mechanical Chemical Gravitational potential Elastic potential Nuclear Heat

THEREFORE, same units apply to all forms!!

Endothermic—

Exothermic—