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General Chemistry > Lecture 2: Gases, Kinetics, and Chemical Equilibrium > Flashcards

Lecture 2: Gases, Kinetics, and Chemical Equilibrium Flashcards

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0
Q

Volume of molecules in gas / Total volume

A

0.1%

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1
Q

Definition of a gas

A

Loose collection of weakly attracted atoms or molecules moving rapidly in random directions

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2
Q

STP

A

Standard temperature and pressure: 0 C and 1 atm

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3
Q

Mean free path

A

Distance traveled by a gas molecule between collisions

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4
Q

Ideal Gas Law

A

PV = nRT

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5
Q

Characteristics of an ideal gas

A
  1. Zero volume
  2. Exert no forces other than repulsive forces due to collisions
  3. Completely elastic collisions
  4. Average kinetic energy of gas molecules is directly proportional to the temperature of the gas
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6
Q

Universal gas constant R

A

0.08206 L•atm / K•mol

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7
Q

Standard molar volume

A

Volume of 1 mole of any ideal gas at STP: 22.4 liters

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8
Q

In a mixture of ideal gases, each behaves as if…

A

…it is alone

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9
Q

Partial pressure

A

Pressure of a gas in gaseous mixture x Mole fraction of that gas

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10
Q

Dalton’s law

A

Total pressure exerted by gaseous mixture = sum of partial pressures of each of its gases

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11
Q

Average kinetic energy

A

= (3/2)RT —ie determined by temperature, not the kind of gas

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12
Q

Graham’s law

A

v1/v2 = sqrt(m2)/sqrt(m1)

v = velocity
m = mass
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13
Q

Effusion

A

Spreading of a gas from high pressure to low pressure through a pinhole

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14
Q

Diffusion

A

Spreading of one gas into another gas or into empty space

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15
Q

Effusion rate equation

A

Effusion rate1 / Effusion rate2 = sqrt(M2) / sqrt(M2)

M = molecular weight

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16
Q

When do real gases deviate from ideal gases?

A

When molecules are close together:

  1. At high pressure, or
  2. At low temperature
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17
Q

Volume of real vs. ideal gas

A

V real > V ideal

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18
Q

Pressure exerted by real vs. ideal gas

A

P real < P ideal

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19
Q

Chemical kinetics

A

Study of reaction mechanisms and rates (ie how quickly equilibrium is achieved)

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20
Q

Collision theory

A

Molecules must collide to react, but most collisions do not result in a reaction

21
Q

2 requirements for a collision to create a reaction

A
  1. Relative kinetic energies of colliding molecules must reach threshold energy (activation energy)
  2. Molecules must have proper spatial orientation
22
Q

Relative kinetic energy

A

Kinetic energy due to relative velocity only; direction matters

23
Q

Why does rate of reaction increase with temperature?

A

Because more collisions with sufficient kinetic energy occur each second

24
Q

Intermediate

A

Product of one reaction, reactant of later reaction in reaction chain; present at very low concentration because unstable, reacts quickly

25
Q

Unit for rate of reaction

A

Molarity per second

mol / L•s

26
Q

What affects rate of reaction?

A

Temperature
Pressure
Concentration of substances

27
Q

Meaning of stoichiometry coefficients in elementary (single step) reaction

A

How many molecules collide to make a reaction

28
Q

Rate law

A

Rate forward = kf[A]^alpha[B]^beta

kf = rate constant for forward reaction
alpha and beta = order of each reactant
alpha+beta = overall order of reaction

29
Q

Rate law by experiment:
2x concentration of reactant A = 2x reaction rate.
What is the order of reactant A?

A

First order

30
Q

Rate law by experiment:
2x concentration of B = 4x reaction rate.
What is the order of reactant B?

A

2nd order

31
Q

Rate law by experiment:
2x concentration of C = 1x
What is the order of reactant C?

A

0 order

32
Q

Rate determining step

A

In a complex reaction, slowest elementary step that determines a reaction’s overall rate

33
Q

If the slow step in a reaction comes first…

A

Slow step determines rate

34
Q

If slow step in a reaction is after the fast step…

A

Slow step still determines rate, but fast step determines the concentration of one or more reactants in the slow step

35
Q

Catalyst

A

Substance that increases the reaction rate without being consumed or permanently altered

36
Q

How does catalyst increase reaction rate?

A
  1. Decreases activation energy, or
  2. Increases steric factor

Provides alternative reaction mechanism that competes with uncatalyzed reaction

37
Q

Heterogenous catalyst

A

Catalyst in different phase from reactants and products (usually solid catalyst for liquid/gas reactants and products)

38
Q

What is the rate law for elementary reaction aA + bB —> cC + dD?

A

Rate forward = kf[A]^a[B]^b

kf = rate constant for forward reaction
a, b = orders of reactants (= stoichiometric coefficients for an elementary reaction)
a+b = overall order of reaction

39
Q

2A + B + C —> 2D

Rate orders:
A: 1st order
B: 2nd order
C: 0 order

What is the rate law for this reaction?

A

rate forward = kf[A]^1[B]^2[C]^0

= kf[A][B]^2

40
Q

Steric factor (p)

A

The fraction of collisions in a reaction having the effective spatial orientation to lead to a reaction

41
Q

Homogenous catalyst

A

Catalyst in the same phase as reactants or products (usually gas or liquid)

42
Q

If concentration of catalyst compared to the concentration of reactants and products is SMALL, increasing the concentration of the catalyst…

A

Increases the rate of reaction

43
Q

If concentration of catalyst compared to the concentration of reactants and products is LARGE, increasing the concentration of the catalyst…

A

Does not affect or only slightly increases the the rate of the reaction

44
Q

Total rate of a catalyzed reaction

A

Rate = sum of original reaction rate law + catalyzed reaction rate law

(Usually, rate of original uncatalyzed reaction is negligible)

45
Q

How do reactants adsorb to the surface of enzymes?

A
  1. Physically, via van der Waals forces

2. Chemically, usually via covalent bonds

46
Q

Why do molecules bond to the surface of a metal catalyst?

A

Metal atoms at the surface, unlike interior metal atoms, have unfulfilled valence requirements

47
Q

Auto catalysis

A

Reaction generates the catalyst as a product

48
Q

Do ideal gases exhibit condensation?

A

No, because condensation is due to intermolecular attractions, which are neglected for ideal gases

49
Q

Condensation

A

Phase change from gas to liquid

50
Q

How does adding a catalyst change reaction equilibrium?

A

Adding a catalyst does NOT change reaction equilibrium

General Chemistry (2 decks)

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