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Chem 202 > Exam 1 > Flashcards

Exam 1 Flashcards

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1
Q

Endothermic

A

products are higher in energy than the reactants

increase in enthalpy

positive H

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2
Q

Exothermic

A

products are lower in energy than the reactants

decrease in enthalpy

negative H

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3
Q

When is there a negative H?

A

when the reaction is exothermic

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4
Q

When is there a positive H?

A

when the reaction in endothermic

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5
Q

bond enthalpy

A

change in enthalpy that is associated with breaking a particular bond in 1 mole of gaseous molecules

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6
Q

bond enthalpy in polyatomic molecules

A

hard to measure since it requires different amounts of energy to break the second bond versus the first

therefore, we use an average bond enthalpy for polyatomic molecules

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7
Q

What is enthalpy measured in?

A

kJ / mol

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8
Q

examples of intramolecular forces

A

covalent and ionic bonds

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9
Q

Entropy sign

A

S

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10
Q

Enthalpy sign

A

H

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11
Q

Entropy

A

a measure of how spread out or dispersed a systems energy is

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12
Q

Formula for the # of energetically favorable ways molecules can be arranged (W)

A

W = x^n

x= # of cells that can be occupied
n= # of molecules

*relates to entropy

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13
Q

Protein folding and energy

A

decrease in entropy in the system because there are less possible arrangements

reaction is exothermic though so the surroundings experience an increase in entropy

this makes the universal entropy increase

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14
Q

entropy of a perfect crystalline

A

0 since molecules are set in place

allows us to determine the absolute entropy of crystalline solids

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15
Q

free energy

A

energy available to do work

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16
Q

G

A

gibb’s free energy

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17
Q

G < 0

A

spontaneous

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18
Q

G > 0

A

nonspontaneous

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19
Q

G = 0

A

at equilibrium

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20
Q

When does temperature come into play when determining spontaneity?

A

when both H (enthalpy) and S (entropy) are either both positive or both negative

in this case one must consider temperature

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21
Q

athermic

A

not producing or absorbing heat

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22
Q

What information do you use to calculate delta H?

A

bond energies

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23
Q

heat of a reaction

A

the difference in energy between the products and reactants

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24
Q

will the heat of a reaction be positive or negative for exothermic reactions? why?

A

negative since the products are lower in energy than the reactants

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25
Q

unit for entropy

A

kJ / K

  • according to ALEKS
  • may want to update with notes
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26
Q

unit for enthalpy

A

kJ / mol

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27
Q

Why is equilibrium dynamic?

A

there are always forward and backward reactions taking place

equilibrium just occurs when these reactions do not change the overall numbers of reactants and products

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28
Q

Does decreasing volume increase the concentration of products?

A

it depends on if the number of moles of products is less than the number of moles of reactants

system wants to decrease the number of moles which could go in either directions

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29
Q

Does increasing temperature increase the concentration of products in an exothermic reaction?

A

no

adding heat will make the endothermic reaction occur, which is the reverse in an exothermic reaction

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30
Q

Does increasing temperature increase the concentration of products in an endothermic reaction?

A

yes

adding heat will make the endothermic reaction occur, which is the forward in this reaction

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31
Q

When a chemical equation is in dynamic equilibrium what is true?

A
  1. rate of forward reaction = rate of backward reaction

2. concentrations are not changing

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32
Q

relationship between free energy and equilibrium constant

A

(delta)G = -RTln(K)

R = gas constant

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33
Q

what is the gas constant?

A

8.314 J*k/mol

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34
Q

what is the symbol for the equilibrium constant?

A

K

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35
Q

Le Chatelier’s Principle

A

when a stress is applied to a system at equilibrium, the system will respond in a direction that minimizes the effect of the stress

the system will shift

36
Q

shift to the right

A

forward reaction will make more products

37
Q

shift to the left

A

reverse reaction will make more reactants

38
Q

When Q < K …

A

we know we have more reactants, so shifts to the right to make more products

39
Q

When Q > K …

A

we know we have more products, so shifts to the left to make more reactants

40
Q

What happens to K when an endothermic system is heated? Why?

A

increases

now have more products

*check that not Q

41
Q

What happens to K when an endothermic system is cooled? Why?

A

decreases

now have more reactants

*check that not Q

42
Q

What does the saying “the solvent dissolves in water” indicate?

A

a spontaneous reaction

43
Q

Does an increase in temperature lower the activation energy?

A

no

44
Q

Does an increase in temperature increase the rate of a reaction?

A

yes

an increase in temp, increases the # of collisions, so the reaction speeds up

45
Q

Why do we label the x-axis reaction progress instead of time?

A

a reaction can go backwards

46
Q

rate of a chemical reaction

A

how fast a reactant is used up OR how fast a product is formed

47
Q

units of rate of reaction

A

M / s

48
Q

Ways to increase the rate of reaction?

A
  1. temperature
  2. amount of reactant
    * comes down to the # of collisions occuring
49
Q

Is the reaction quotient at equilibrium?

A

no

50
Q

Q = K

A

equilibrium

51
Q

sublimation

A

phase change from a solid to gas

endothermic because need to overcome dispersion forces in solid state (+)

entropy also increases from solid to gas (+)

so, if the reaction is spontaneous comes down to temperature

52
Q

Which thermodynamic situation is entropy driven?

A

when enthalpy is positive and entropy is positive, but reaction is spontaneous at high temperatures

53
Q

Which thermodynamic situation is enthalpy driven?

A

when enthalpy is negative and entropy is negative, but reaction is spontaneous at low temperatures

54
Q

example of a MACROSTATE

A

a phase

solid, liquid, or gas

55
Q

Why do proteins fold spontaneously?

A

their is no change in enthalpy because the hydrogen bonds made between itself are balanced by the hydrogen bonds lost with between the protein and water

entropy is positive because of the water

before folded, the water has to organize itself around the amino acid chain in a very structured way

after folded, the water is more disorganized, which allows entropy to drive protein folding and make it spontaneous

56
Q

kinetics defintion

A

path dependent mechanisms

57
Q

thermodynamics defintion

A

dependent on energy difference between reactants and products

path does not matter

state function

58
Q

state function defintion

A

defined as a property that only depends on the initial and final state of a system

59
Q

How can a reaction occur even is the energy level is below the activation energy?

A

energy is an average and individual atoms can have enough energy to make the reaction occur

60
Q

What two factors are important for a reaction to occur?

A

amount of energy and orientation

61
Q

How to calculate K for the reverse reaction, given K of the forward reaction?

A

1/K

62
Q

How to calculate K for an equation multiplied by a number?

A

(K)^n

63
Q

Why did the box freeze to the beaker in class example?

A

Because endothermic reactions take energy/heat from their surroundings

64
Q

Why is there a needed amount of activation energy?

A

Energy is needed to break the bonds in the reactants before you can form new bonds in the products

65
Q

Best possible orientation for collisions to happen

A

When particles are moving directly towards each other they will have greater impact and provide more energy to the reaction

66
Q

Why does the rate of the reaction increase with temperature?

A

when temperature increases a greater number of particles have energy in excess to the activation energy so there is a greater probability of the reaction occurring

67
Q

Misconception about temperature and rate of reaction

A

Particles move faster which makes collisions more likely

This is true, but not the main reason why

68
Q

What happens when you double the concentration of a reactant?

A

The rate of reaction is doubled

69
Q

Enthalpy

A

Sum of internal energy plus pressure and volume of the system

70
Q

Gibb’s Free Energy

A

The energy that is available to do work

71
Q

Enthalpy of phase change

A

All phase changes are accompanied by changes in enthalpy, since there is a change in energy levels

For example, melting is an endothermic process and freezing is an exothermic process

72
Q

The hydrophobic effect

A

When water arranges itself around two separate non-polar molecules, water is highly structured

When water arranges itself around one combine non-polar molecules, water is not as structured and disorder increases

Entropy driven change

73
Q

Energy changes between physical and chemical changes

A

Physical changes include phase changes, so there is a change in enthalpy and energy levels. Breaking intermolecular forces

Chemical changes involve the complete breaking of intramolecular bonds, so there are larger changes in energy levels

74
Q

List types of bonds in order of decreasing strength

A

Ionic

Covalent

Dipole-dipole

75
Q

Temperature

A

a property of matter that describes the energy of motion of component particles

comparatively measures hotness and coldness based on an absolute zero

76
Q

Law of Mass Action

A

the principle that the RATE of a chemical reaction is proportional to the masses of the reacting substances

77
Q

What two things do changes in temperature alter?

A

The rate of the reaction

The equilibrium coefficient (k)

78
Q

How does a catalyst affect a reaction?

A

it increases the rate of the reaction by lowering the amount of activation energy needed

79
Q

How many kJ per kcal?

A

4.184 kJ / kcal

80
Q

Why is combustion an exothermic reaction?

A

Because heat is released

81
Q

What happens when volume is decreased?

A

there is an increase in the partial pressure of all the substances

so, system shifts to least number of moles to compensate

82
Q

what happens when there is an increase in volume?

A

there is a decrease in partial pressures of all substances

system is free to expand to greater number of moles

83
Q

If nonspontaneous what must one do?

A

Continue supplying energy to the system in order for the reaction to occur

84
Q

Why does the law of mass action exclude pure liquids and solids?

A

Their concentrations do not change

If I have a ton of water or a drop of water it still has the same molarity

85
Q

What happens when heat is added to a reaction?

A

The rate of both the forward and reverse reactions is increased due to more kinetic energy and more collisions

However, the increase in kinetic energy will effect the larger activation energy more

That is why when exothermic reactions are heated they go the opposite direction because the products have lower energy than the reactants

Chem 202 (7 decks)

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