Well cut through this one. :)

CHOPPED-UP CHAPTER

ENERGYCHAPTER 10

WHAT DO YOU KNOW?

What first comes to your mind when you hear the term energy?

What do calories measure?

List three sources of energy.

Have you heard of the term entropy? What does it mean?

HERE WE WILL...

understand the general properties of energy

understand the concepts of temperature and heat

understand the direction of energy flow as heat

10.1 THE NATURE OF ENERGY

Energy is the ability to do work or produce heat

can be classified as kinetic or potential

kinetic = energy due to motion

potential = energy due to position

one of the fundamental characteristics of energy is that it is conserved

it is changed in form but not created or destroyed in a typical rxn

this the law of conservation of energy

S

10.2 TEMPERATURE AND HEAT

the temp of something is a reflection of the vigor of the random motions of the components of that substance

heat is a flow of E between two objects due to a temp difference in the two objects

notice here that matter has a boundary; energy does not

on the next slide, notice that there was a heat flow b/t the two sides that were different Ts

which way did it flow?...

the random motions of the components of an object constitute the thermal energy of that object

the flow of energy called heat is the way in which thermal energy is transferred from a hot object to a colder object

10.3 EXO- AND ENDOTHERMIC

what is this????

in an exothermic rxn,E flows from system surroundings

in an endothermic rxn,E flows from surroundings system

exo often feel warmer (like fire);endo often feel cooler

FRINKING FRAP TIMEExo or Endo process? (from point of view of bold things)

1. Your hand gets cold when you touch ice.

2. The ice melts when you touch it. (think!)

3. Ice cream melts.

4. Propane burns in a propane torch.

5. After swimming, water drops on your skin evaporate.

6. Two chemicals mixing in a beaker give off heat.

WALK AWAY WITH...1A

energy is conserved

the law of conservation of energy says that energy is neither created nor destroyed in a chemical process

energy can be changed from one form to another but the total amt of E remains the same

WALK AWAY WITH...1B

energy is classified as either kinetic or potential

kinetic due to motion, potential due to position

WALK AWAY WITH...2

temperature indicates the vigor of the random motions of the components of that substance

heat is the flow of energy b/t two objects b/c of a temp diff

exothermic is where heat flows from system to surroundings

endothermic is opposite

HERE WE WILL...

understand how heat is measured

understand energy as a driving force for natural processes

understand the basic concept of entropy

10.4 THERMODYNAMICS

thermodynamics is the study of E and its changes from Gk therme (heat) + dynamiks (force or power)

internal E of a system is the sum of the kinetic (due to motion) and the potential (due to position) Es of a substance

10.5 MEASURING ENERGY CHANGES

a calorimeter [L. calor = heat] is used to measure the heat of chemical reactions

units used are joules (but also calories)

(low joule products)

to measure E changes you need to know 1) the T change (C) of your sample...

(which takes more energy: to heat this pool by 10C or by 20 C?)

and 2) the amount of substance being heated (g)...

(Which takes more energy? to heat this cup of water 10C or the pool?)

and 3) the specific heat capacity of a substance

i.e. E required to change the temp of 1 gram by 1 degree C

water has an enormous heat capacity (4.18 J/gC),sand not so much (0.8 J/gC)...

thats why wet sand is so much cooler and easier to walk through on a hot day than dry sand - same amount of sunlight, but the water absorbs a lot of heat as its temp rises slooooowly

which is why we can do this

all three (mass, change in T, sp/heat/cap) can be used to calculate the changes in energy that occur in reactions or special circumstances ready?

Q = smT Q = heat (J)

s = specific heat capacity (a constant, measured in J/gC)

m = mass (g)

T = change in T (C)

EXAMPLE

1.6 g of a mystery gold-like metal requires 5.8 J of energy to change its T from 23C to 41C. Is it gold? (sAu = 0.13 J/gC)

solve for s, so:

s = Q/mT

s = 5.8/(1.6 x 18)

s = 0.20 J/gC, so not gold!

QUICK QUIZYou want to heat a mug of tea (250 g) from room temp, 25C to 100C.How much E would you need? (sH2O for water = 4.184 J/gC)

Q = smT

Q = (4.184)(250)(75)

Q = 78,000 J

Q = 78 kJ

10.10 ENERGY AS A DRIVING FORCE

Why does a log burn to ash, but ash never gathers to make a log?

Why does a toot spread throughout a room, but not gather in one place again?

two important things weve figured out in science:

nature likes to spread energy around

nature likes to spread matter around

If both energy spreading and matter spreading take place, your reaction will go. (like an explosion)

If neither, then it wont happen by itself. (like CO2 and H2O getting together to make sugar)

If both are competing, like hydrogen and oxygen getting together (bad) but giving off energy when it does (good!) it depends on other things like temperature. (too complicated to figure out now)

but what is this matter spreading out business?...

ENTROPY

entropy (S) is a way of keeping track of the randomness of a process

the lower the entropy the more ordered it is (like ice or a Lego creation)

the higher the entropy the more disordered (like steam or your room)

since the tendency is for E and matter to spread, the entropy of the universe is increasing.

= second law of thermodynamics

thus the universe is headed toward total randomness. Woo oho!

:)

WALK AWAY WITH...1

thermodynamics is the study of energy and its changes

the common units for heat are calories and joules

the amount of heat (Q) involved can be found

Q = smT

WALK AWAY WITH...2

natural processes occur in the direction that leads to an increase in the disorder (increase in entropy) of the universe

the principal driving forces for natural forces can be described in terms of matter spread or energy spread

10EOCS

14, 24, 26, 52