Notesale: Turn your study into money

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Specific Heat Capacity and Calorimetry —>
DEF --> Amount of energy needed to heat one gram of a substance by one degrees Celsius

we would be measuring temperature change and using melting etc
Scenerio

How we should set this up-->
exothermic process = alloy real easing heat to the water
endothermic process = water absorbing best from the alloy
q of the metal (will be negative) = -q f the water (will initially be positive)

use M C delta T (metal) = - C M delta T (water)
**delta T = final temperature - initial temperature
can fill in the mass and the delta T or temperature
we know the specific heat of the water and so once we fill that in we can solve for the c of
the metal which is
...
221kJ/K
T = 252ºC + 273 = 525K
∆G = -157kJ - 525K * -0
...
221kJ/K
Ans = ∆G = -41kJ
the answer is less than 0 therefore this reaction is spontaneous
if ∆G is zero than the system is at equilibrium

∆H

∆S

∆G

spontaneous

-

+

always -

yes

+

-

always +

no

+

+

either + or -

sometimes

-

-

either + or -

sometimes

Spontaneity —>

this does not tell us why a chemical reaction occurs
the energy doesn't disappear it just gets transformed form one form to another
this helps us understand that the net energy is not changing

^-- this is the chemical definition
Examples of Spontaneous Processes:

if something is spontaneous than the reverse of that is not spontaneous (aka the reverse
does require energy)
these examples are spontaneous but the reverse of them does require energy

essentially the reverse of spontaneous change
**spontaneous change does not mean that it happens quickly
Why are some Processes Spontaneous
primary possibility is that it corresponds to enthalpy
exothermic process (∆H < 0)
can be spontaneous
endothermic process (∆H > 0)
can be spontaneous
since they both can be spontaneous this does have something to do with enthalpy but not

only entropy

in any endothermic change we need a positive entropy change in order for the process to be
spontaneous
SO

It is positive if disorder increase and negative if disorder decreases
if confused look at the gases because they contribute much more to the entropy
* degrees symbol means it is standard state
Answers:
positive
negative
positive

negative
positive
positive
negative
negative
for calculating the enthalpy change there is no ∆ because everything has entropy (except for a
perfect crystal at absolute zero), therefore you can measure absolute entropy
Entropy —>
Spontaneous Change is something that occurs naturally without a continuous input of temperature
if something is spontaneous in one direction it is not spontaneous in the other reaction
EX: candle burning, bike rusting, etc
...
reorder
1
...
Cu + CuO --> Cu2O ∆H=11kJ
3
...
2Cu2O + O2 --> 4CuO ∆H=-288kJ
2
...
cancel
1
...
2Cu + --> ∆H=-22kJ

7
...
2Cu + O2 --> 2CuO ∆H=-310kJ
9
...
-310kJ
Thermochemistry —>
Potential Energy:
All matter contains potential energy that comes from position
Chemical Potential energy is energy due to position on the molecular or even atomic level
In a rection electrons can release or gain potential energy
when energy is produced in a reaction the reactants have more potential energy at the start
and so they give some of it to the product

^-- first law
also says that matter is neither created nor destroyed

blue water also as energy
Graphing Energy:
going from N2+O2 --> 2NO you will have a curve that starts low has a little bump and then
ends higher because it is releasing energy
Energy Transfer

****work is the force across a distance
*********but we are focusing on thermal chemistry which is only the heat
constant pressure means there is no work and that is what we are doing
when energy is transformed it is going to be in the form of heat (endo or exto)

1
...
heat flow into the system (always positive)

this makes sense because energy is released in the form of heat so in the exothermic graph
there would be less energy at the end than at the start
enzymes changes the curve/lower the activation energy to make it occur faster but it doesn't
change the energy difference between the energy of the products and reactants
property isn't based on the pathway

enthalpy is a
state function

1
...
oxogen is excess bc it says in the problem excess oxogen
ans
...
1 mol is half of 2 so you just divide 1652 by 2 and u get the answer which is 826kJ
4
...
40kJ
5
...
4kJ
Standard Enthalpy of Formation —>

elements who are already in their standard state have ∆Hf of 0

we measure enthalpy as its changes so some things are defined as zero and the others are
based on that
the enthalpy formation is just the number that states how much energy is released or
absorbed when something is created

ex1:
H2(g) + 1/2O2(g) --> H2O(l) ∆Hf degrees = -285
...
5kJ/mol of cloroform

Cgraphite(s) --> Cdiamond(s)
∆Hrxn = ∆Hf Cdiamond - ∆Hf Cgraphte ***if there wed coefficients than in the next step you
would hev tot multiply the energy
∆Hrxn = 1
...
9kJ



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