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Bio and Chem 12 > Chemistry Chapter 1 > Flashcards

Chemistry Chapter 1 Flashcards

1
Q

Define chemical kinetics

A

The investigation of the rate at which chemical reactions occur and the factors that affect them.

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2
Q

What are some considerations when measuring reaction rate?

A

-is there a measurable property associated with the change in quantity of a reactant or product you might use to determine the rate?
-exactly how might you measure the quantity of reactant or product in the lab
-what units would be associated with the quantity you measure and what units represent the reaction rate

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3
Q

What is the formula to calculate average reaction rate?

A

change in a measurable quantity of a chemical species/change in time

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4
Q

What are some examples of reaction kinetics?

A

Measuring the change of mass in a solid, volume of gas produced, and change of pressure in a system

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5
Q

What is the direct method?

A

When the reactant or product involved in a reaction can be measured directly ex: volume of gas produced with a eudiometer, pH indicators, spectrophotometer

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6
Q

What is the formula for reaction rate

A

final concentration-initial concentration/final time-initial time

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7
Q

What is a homogeneous reaction?

A

Reactants are in the same phase and mix/collide easily ex: gases, dissolves solutes, or aqueous substances

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8
Q

What is a heterogeneous reaction?

A

Reactants are in different phases and do not mix/collide easily eg: solid and gas, solid and liquid, liquid and gas, 2 solids are called a mechanical mixture because they can be physically separated

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9
Q

Do heterogeneous or homogeneous reactions have a faster reaction rate?

A

Homogenous reactions are faster because the particles collide and mix faster due to being in the same phase.

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10
Q

What is collision theory?

A

Every chemical reaction is the result of a collision between reactant molecules or atoms

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11
Q

What is needed to form product?

A

Enough kinetic energy and the appropriate geometry

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12
Q

What will increase reaction rate?

A

Increasing the number of collisions and energy of collisions

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13
Q

How does increasing reactant concentration increase reaction rate?

A

-increases number of particles able to react
-increases frequency of collision between particles

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14
Q

How does increasing surface area of reactants increase reaction rate?

A

-increases the number of particles and collision sites that are exposed and available to react which increases frequency of collisions

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15
Q

How does increasing temperature increase reaction rate?

A

-increases kinetic energy which increases frequency of collisions

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16
Q

How does the nature of reactants affect reaction rate?

A

-ionization energy, electronegativity, ionic and molecular polarity, size, complexity of structure, can make it more or less reactive

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17
Q

How do catalysts increase reaction rate?

A

-increase reaction rate without being used up
-remain same quantity when the reaction is completed
-provides correct geometry and activation energy needed for collisions

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18
Q

What does collision theory state that reaction rates depend on?

A

-the number of collisions per unit time
-the fraction of these collisions that succeed in producing products

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19
Q

What are successful/effective collision requirements?

A

-minimum kinetic energy/activation energy
-proper orientation

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20
Q

How can catalysts decrease activation energy?

A

a) enzymes in living systems: allow reactions to take place at low temps (37)
b) many different metal surfaces: palladium and platinum in catalytic converters

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21
Q

What are some things catalysts must do?

A

-increase the number of effective collisions by providing correct geometry
-provide a reaction path with a lower activation energy
-will be consumed only to regenerate in a later step

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22
Q

What are the parts of a binding catalyst?

A

substrate: the part that enters the catalyst
active site: where the substrate fits in

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23
Q

What is enthalpy?

A

Potential energy that may be evolved (given off) or absorbed as heat

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24
Q

What causes the enthalpy stored in reactants to differ from that in products of physical or chemical change?

A

Chemical bonds, the chemical potential energy derived from the position of negative electrons relative to the positive nuclei and nearby nuclei is called the bond energy

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25
What does bond energy require?
-energy input, bond forming results in energy release
26
What are endothermic reactions?
When the energy absorbed to break bonds is greater than the energy released during bond formation, positive delta H values
27
What are exothermic reactions?
When mire energy is released during bond formation than absorbed during bond breaking, negative delta H values
28
What is a thermochemical equation?
Includes the energy change as an integral part of the chemical equation while delta H notation requires the energy change to be written after the equation with a delta H symbol
29
What is an activated complex?
An intermediate state that is formed during the conversion of reactants into products. The activated complex forms when potential energy is at a maximum and kinetic energy is at a minimum during a reaction.
30
What is a potential energy diagram?
Graphical representation of the energy changes that take place during a chemical reaction. The enthalpy changes can be followed along the vertical axis which measures potential energy in kJ/mol. The horizontal axis is called the progress of reaction (not time!)
31
What is the activation energy on a PE diagram?
The difference between the PE of the activated complex and the total PE of the separated reactant molecules
32
What is the enthalpy change on a PE diagram?
PE of products - PE reactants
33
Is activation energy lower for endothermic or exothermic reactions?
exothermic!
34
What factors do not affect potential energy?
temperature, pressure, concentration, and surface area
35
What does affect potential energy?
catalysts: they will form more than one activated complex so there is more than one peak in the diagram
36
What are reaction mechanisms?
Series of steps that may be added together to give an overall chemical reaction, each individual step is called an elementary process
37
What are the number of reactant species?
-unimolecular: reaction involving 1 molecule -bimolecular: reaction involving the collision of 2 molecules -termolecular: reaction involving 3 molecules (extremely rare)
38
What is an intermediate?
A species that is formed in 1 step and consumed in a subsequent step and so does not appear in the overall reaction ex: catalyst
39
What is the rate-determining step?
The slowest elementary process that the reaction rate cannot exceed
40
What conditions in the rate-determining step cause a limit to the overall reaction?
-complex collision geometry -high activation energy -low concentrations of reactants -a termolecular collision
41
Which step must you increase reactant concentration in?
the rate-determining step
42
Where is the rate-determining step on a PE diagram?
the highest peak and the number of peaks shows the number of steps in the mechanism
43
When does chemical equilibrium exist?
When the forward rate of chemical reaction equals its reverse rate
44
For a system to be at chemical equilibrium it must:
-have constant macroscopic properties eg: colour of reaction stays same -be a closed system -"shift" when conditions are changed by a stress
45
Conditions for chem. equil. to exist
a) rate of forward and reverse reactions are equal b) we must have a reversible reaction c) must be a closed system d) the temp. of the system is constant e) because of d, pressure is also constant
46
How to recognize equil.
-if the observation shows no changes in colour, mass, pressure, volume, or any other observable property on the macroscopic level
47
Why can a reaction rate not be 0?
The rate at which the reactants are being consumed equals the rate at which they are being reformed
48
What are the main characteristics of an equil. system?
a) will remain at equilibrium unless reaction conditions are changed b) the state of equilibrium can be approached from either direction c) if the system is disturbed, it will move to re-establish equilibrium
49
What happens as a reaction proceeds?
-the reactant concentrations decrease so the forward rate (fr) decreases -in a closed system, the product concentrations also rise so the reverse rate (rr) increases -this continues until rr=fr
50
What are the 3 stages of reaching equilibrium?
1: as reaction begins, high reactants generate a fast forward reaction 2: as the reactants fall, so does the forward rate while the products rise with the reverse rate 3: this continues until the reverse rate equals the forward rate and equilibrium has been established
51
What will an equilibrium system do when subjected to stress?
It will shift to partially alleviate the stress and restore equilibrium
52
What will an equilibrium system do when reactant or product is added?
Shift to remove some of the added chemical
53
What will an equilibrium system do when reactant or product is removed?
Shift to replace some of the lost chemical
54
What is stress to an equilibrium system?
Any action that has a different effect on the forward reaction than it does on the reverse reaction and thus disrupting equilibrium ex: adding reactant increases forward reaction rate, adding product increases reverse reaction rate
55
What is Le Chatelier's Principle?
-when a system in a state of dynamic equilibrium is acted on by some outside stress, the system will, shift if possible to a new position of equilibrium to minimize the effects of the stress
56
Factors affecting equilibrium:
a) pressure: increasing pressure causes the system to shift to the side with fewer gas particles b) concentration: increasing reactant concentration can cause the system to shift towards products, increasing product causes shift towards reactants c) temperature: increasing temp favours endothermic reaction (forward), decreasing favours exothermic (reverse) d) catalysts: can cause equilibrium to be reached quicker
57
How do equilibria react to volume changes?
-by shifting to relieve some of the added pressure or to replace some of the lost pressure, increased volume causes decreased pressure -equilibria will shift to the side with fewer gas particles, decreased volume causes increased pressure
58
How does an increase in surface area effect equilibrium in heterogeneous reactions?
Increases forward and reverse rates equally hence equilibrium doesn't shift
59
How do equilibria react to temperature changes?
-by shifting in the endothermic direction to remove some of the added kinetic energy (heat) or in the exothermic direction to replace some of the lost kinetic energy (heat)
60
What is entropy?
A substance's or system's state of disorganization or randomness
61
List examples of low entropy
-organized, simple, atoms with few electrons, m/c with few atoms, pure substance, substance at low temp, solid
62
List examples of high entropy
-disorganized, complex, atoms with many electrons, m/c with many atoms, mixture, substance at high temp, gas
63
What are 2 thermodynamic drives influence on an equilibrium's position?
1. The drive toward decreasing enthalpy (ex: in the exothermic direction) 2. The drive toward increasing entropy or disorder
64
When do increases in entropy happen?
-increase in number of product gas molecules over reactant gas molecules -formation of a gas from a liquid or solid -a solid or liquid dissolving
65
When does no reaction occur?
-when entropy is decreasing (higher entropy favours reactants because reactants have more gas particles) -enthalpy is increasing (lower enthalpy favours reactants because the reactants have lower PE) -the reactants are favoured so there is no reaction
66
When does completion occur?
-higher entropy favours products because there are more gas particles -lower enthalpy favours products because the products have lower PE -products are favoured and the forward reaction occurs spontaneously to completion
67
When does equilibrium occur?
-higher entropy favours products because there are more gas particles -lower enthalpy favours reactants because they have lower PE -the products have greater entropy and reactants have lower enthalpy which means the reaction will be at equilibrium
68
What is the equilibrium constant?
For any equilibrium reaction, at a certain temperature, the equilibrium ratio of product concentration to reactant concentration will always be the same (constant)
69
How do you make an equilibrium expression?
product concentration/reactant concentration -addition becomes multiplication -left side always reactants, right always products -only include gas states or aq -coefficient becomes exponent
70
What is the only factor that can change a constant equilibrium?
decreasing temp increases equilibrium constant
71
What is important info that Keq gives?
a) large Keq means forward reaction is favoured ex: products > reactants b) small Keq (<1 but not negative) means reverse reaction is favoured ex: reactants > products c) if Keq is close to 1 then neither reaction is favoured and reactants is almost equal to products
72
What can affect Keq?
-doubling, tripling all coefficients will square or cubed the Keq -reversing the equation causes Keq to be inverted ex: 1/Keq
73
What is trial Keq or reaction quotient?
The numerical value derived when any set of reactant and product concentrations (not equilibrium concentrations) is plugged into an equilibrium expression
74
What happens if trial Keq is smaller than actual Keq?
the reaction must shift towards the products, there are too much reactants and not enough products
75
What happens if trial Keq is bigger than actual Keq?
the reaction must shift towards the reactants, not enough reactants and too much product
76
What are 3 related values in any chemical system that develop into an equilibrium?
-the equilibrium constant -the initial concentrations -the equilibrium concentrations
77
What are 2 chemical concepts used to solve equilibrium problems?
-reaction stoichiometry: the mole ratio in which reactants are consumed and the products are formed -the equilibrium law: the relationship between the equil. constant and and any set of equil. concentrations
78
What is a RICE table?
r: reaction (including phases) i: initial concentrations (mol/L) c: change in concentration (due to equilibrium shift) e: equilibrium concentrations

Bio and Chem 12 (4 decks)

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