Chemistry Heat, Work, and Energy

Exam 4

Example: Heat + Sodium Metal

1- things fly —> kinetic energy

2- chemical reaction

3- flames —> thermal energy

4- Product + beaker heat up —> thermal energy

Kinetic Energy

energy of things due to their velocity

Thermal Energy

energy caused by atoms moving past eachother

Potential Energy

energy of things due to where they are (top of a table with the ability to fall off)

System (energy transfer situation)

gives or receives energy (often the smaller object and is the object of interest)

Surrounding (energy transfer situation)

everything else

Open vs Closed (between system in surrounding)

open → matter can be exchanged

closed→ matter can not be exchanged

Isolated (not between system and surrounding)

neither matter nor energy can be exchanged

Exchange of energy

work a system can do (expansion or compression under constant pressure)

(chemically through a reaction or physically through an object)

ex: force applied over a distance

Chemical Exchange of Energy (equation)

W= -PΔV

w: work is the force applied over a distance

-P: pressure

ΔV: volume (vfinal-vinitial) vfinal looks like it should be the vinitial

Identify use by checking for change in volume (volume has to change in order to use this equation)

unit= joules (J) (kgm^2 S^-2)

Physical Object Exchange of Energy (equation)

W= -FΔx

Water Constant

Cwater = 4.184 J/g*K (Kelvin or Celsius depending on what you are utilizing)

Compression

work > 0

Expansion

Work < 0

Heat (q)

: energy exchanged w/o work

does not simply refer to temperature unit is J

Processes Involving Heat

Temperature Change

Phase Change (l)(aq)(s)

Chemical Reactions

Conversion of atmJ to Joules

J = 100atm x 1atmJ

multiply by W (atmJ) with 100atm to get J alone

(100 atm per every atmJ)

When comparing a systems heat (q) or Work (w) to surroundings heat or work …..

set the equations equal to each other and ONE SIDE HAS TO BE NEGATIVE (usually surrounding)

set up like

qsys = -qsurr

wsys = -wsurr

then use either equation for work(w) or for heat (q)

Heat (q) equation (heat and temperature relationship)

q = CΔT

q = heat

C = Heat Capacity (sometimes little c for specific heat capacity) or (cm for molar specific heat capacity)

ΔT = Change in temerature (Tf - Ti)

Calorie

the energy required to raise a gram of water at 20*c by 1*c

when given calories and temperature (celcius or K) 1 calorie: 4.185J / g*c

when given calories and grams of something: 1.00cal / g*c

c being degrees celcius

Phase Change equation

q = nΔH