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chem > Unit 5 > Flashcards

Unit 5 Flashcards

1
Q

Heat of formation formula

A

ΔH° = Sum of ΔHf°(products) - Sum of ΔHf°(reactants)

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2
Q

calorimetry formula

for solids, liquids, gases

A

q = mcΔT

t = final temp-initial temp

c = specific heat capacity, divide by 1000 to convert j to kj

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3
Q

calorimetry formula

for melt

A

q= nHfus

n = no. of moles, Hfus = given value

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4
Q

calorimetry formula

for vaporization

A

q= nHvap

n= no. of moles, Hvap = given value

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5
Q

bond energy formula

A

ΔH = ∑H(bonds broken) - ∑H(bonds formed)

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6
Q

Internal Energy, E

A

sum of kinetic and potential energies of all “particles” in a system

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7
Q

Potential energy

A

energy of position

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8
Q

Kinetic energy

A

energy of motion

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9
Q

Temperature

A

a measure of the random motions of the atoms or molecules of a substance

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10
Q

Temp. (in kelvin) relationship to KE

A

directly proportional to the kinetic energy of the molecules or atoms

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11
Q

Heat

A

a flow of energy between two objects due to a temperature difference between the objects; the way in which thermal energy is transferred

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12
Q

First law of thermodynamics

A

energy in the universe is constant; energy (heat) cannot be created nor destroyed

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13
Q

System

A

part of the universe on which we focus attention (the products and reactants)

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14
Q

Surroundings

A

everything else in the universe

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15
Q

Exothermic

A

Energy is being released by the system (change in heat is neg.)

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16
Q

Endothermic

A

Energy is being absorbed by the system (change in heat is pos.)

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17
Q

Heat of formation

A

the energy that accompanies the formation of one mole of a substance at STP(25°C); values for some elements and compounds are given

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18
Q

Standard temperature for thermodynamics

A

25°C

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19
Q

Heat of formation for element in its natural state

A

ZERO

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20
Q

Specific heat capacity (c)

A

the amount of heat required to raise the temperature of 1 gram of a substance by 1°C (given value)

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21
Q

ΔT

A

Tfinal-Tinitial

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22
Q

Why doesn’t temp. increase on plateau parts of graph?

A

It takes a lot of energy to change a phase, so energy is devoted to the phase change rather than an increase in temperature

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23
Q

Hess’ Law

A

the change in enthalpy is the same whether the rxn takes place in one step or a series of steps

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24
Q

Entropy (s)

A

function which keeps track of the tendancy for the components of the universe to become disordered; measure of disorder/randomness/chaos in the universe

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25
states of matter w/ entropy
solid
26
Second law of thermodynamics
the entropy of the universe is always increasing; process that increases entropy (ΔS+) is favorable
27
Processes that increase entropy
- dissolving - inc. in temp. - phase change solid --> liquid --> gas - inc. no. of moles of gas
28
entropy formula
ΔS = ∑S(products) - ∑S(reactants)
29
Why does dissolving increase entropy?
ex. when salt dissolves into water, salt breaks down into ions, ions floating in aqueous solution is more disordered than solid
30
Why does increase in temp. increase entropy?
molecs/atoms move more quickly (also could change phase) --> more disorder
31
Why does increase in moles of gas increase entropy?
the more gaseous moles, the more disorganized the molecules are moving
32
Spontaneous rxn
rxn that occurs w/o outside intervention
33
Spontaneous process formula
ΔG = ΔH - TΔS
34
Gibb's free energy (ΔG)
if ΔG is neg., rxn is likely to be spontaneous, if ΔG is pos., rxn will not be spontaneous
35
when ΔG is favorable
ΔG is neg.
36
When ΔS is favorable
ΔS is pos.
37
when ΔS = + and ΔH = -
always spontaneous
38
when ΔS = - and ΔH = +
not spontaneous
39
Unit of entropy
Joules/kelvin (J/K)
40
Unit of G
Joules (J)
41
Kelvin to celsius
K = C + 273
42
when both ΔH and ΔS are not favorable
not spontaneous
43
if one of ΔH and ΔS are favorable
spontaneity depends on temp
44
what does nonspont. rxn require
catalyst
45
why is neg. enthalpy (ΔH-) favorable for spontaneity?
exothermic rxn; endo. is dependent on smth in surroundings to provide energy so cannot occur on its own
46
what entropy favorable?
inc. in entropy (ΔS+) (entropy always increasing in universe)
47
What does Gibb's Free Energy measure?
likeliness of spontaneous reaction to occur
48
Kinetics
the study of how fast reactions go to completion; rate at which product is formed
49
temp. to rxn rate correlation
temp. are rxn rate are directly proportional
50
factors that effect rxn. rates
- temperature - concentration - surface area (SA) - agitation - catalyst
51
How does increase in temp. increase rxn rate?
increase in temp--> particles move faster--> particles collide more often (inelastic collisions)--> rxn. rate increases
52
Concentration
no. of particles in a given volume
53
How does increase in concentration increase reaction rate?
inc. in concentration--> more particles in a given volume--> more collisions--> inc. rxn. rate
54
how does increase in surface area increase rxn rate?
smaller particle size--> larger SA bc/ more of 1 chemical cn touch the other--> more collisions happen quickly--> increased rxn rate
55
surface area
the amt that one chemical can touch another; the smaller the particle size, the larger SA; ex. sugar cube vs packet dissolving in water
56
agitation
shaking, swirling, etc.
57
how does agitation increase rxn rate?
inc. agitation--> forced collisions--> more collisions happen quicker--> rxn rate increases
58
catalyst
a chemical that speeds up a rxn by lowering the amt. of activation energy needed to start a rxn thereby lowering the energy of the activated complex (w/o) being consumed
59
opposite of intermediate
catalyst- added in the first step and reproduced in the last step
60
activation energy (Ea)
energy needed to start a reaction
61
activated complex (AC)
intermediate species in which its bonds are being stretched but not yet broken
62
what happens if there's enough activation energy
new bonds form in rxn
63
catalytic pathway
pathway on graph that differs from rxns without a catalyst
64
draw potential energy diagram for endo. rxn.
65
draw potential energy diagram for exo. rxn.
66
what happens to the slope when catalyst added
slope does not reach original activated complex
67
does catalyst change energy of product or reactant
no :)
68
Equilibrium
the state of which the forward reaction is equal to the rate of the reverse reaction; concentrations of all products and reactants remain constant with time once equilibrium has been established at constant temperature
69
when are reactions reversible
at equilibrium
70
how are reversable rxns. indicated
double headed arrows
71
dynamic
when the graph lines level out; indicates that equilibrium has been established and concentrations of reactants and products are constant
72
draw concentration graph where equilibrium is established
just check and make sure its right
73
LeChatlier's Principle
when a system at equilibrium is disturbed by a stress, it tries to attain a new equilibrium position that minimizes the stress by shifting away from an increase or towards a decrease
74
examples of stress that can disturb equilibrium
- change in concentration - change in temperature
75
shifting forward
producing more product
76
shifting in reverse
producing more reactant
77
change in concentration
an increase in concentration of the reactant or product is a stress on the equilibrium of the system; causes inc. in collision frequency + rxn. rate
78
change in temperature in equilibrium
equilibrium shift depends on whether the rxn is endo. or exo. if rxn is exo: heat will act as product bc/ its being released if rxn. is endo: heat will act as a reactant bc/ its being absorbed
79
draw diagram of equilibrium rxn. when more reactant is added
[insert photo]
80
draw diagram of equilibrium rxn. when more product is added
[insert photo]
81
draw diagram of equilibrium rxn. when more reactant is removed
[insert photo]
82
draw diagram of equilibrium rxn. when more product is removed
[insert photo]
83
units of specific heat capacity
J/kg°C or J/kjK
84
eqn. for equilibrium constant

chem (3 decks)

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