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Chemistry 101 > Energy, Rate, & Equilibrium > Flashcards

Energy, Rate, & Equilibrium Flashcards

1
Q

What is thermodynamics?

A

Study of energy, work, and heat

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2
Q

What are the 3 thermodynamic laws?

A

1) energy cannot be created or destroyed only converted from one form to another
2) universe spontaneously tends toward increasing order/ randomness
3) disorder of a pure, perfect crystal at absolute zero (0 kelvin ) is zero

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3
Q

What are basic concepts from kinetic molecular theory?

A
  • Molecules & atoms in a reaction mixture are in constant, random motion
  • molecules & atoms frequently collide with each other
  • only some collisions (those with enough energy) will break bonds in molecules
  • when reactant bonds are broken, new bonds may be formed & products result
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4
Q

What is the difference between system and surrounding?

A

System: contains process under study
Surroundings: rest of universe
Systems + surrounding → universe
Can determine energy of surrounding not system

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5
Q

What chemical reactions can happen to energy in systems and surroundings?

A
  • Energy can be lost: system → surrounding

- Energy can be gained by system at expense of surrounding (usually in form of heat that measured in temperature)

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6
Q

What is the first law of thermodynamics?

A
  • energy of universe is constant
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7
Q

What happens in chemical bonds?

A

A-B + C-D →A-D + C-B
Each chemical bond is stored chemical energy
If reaction will occur: bonds must break & breaking bonds requires energy
Forming new bonds → release energy

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8
Q

What is an exothermic reaction?

A

A-B + C-D →A-D + C-B + energy
If energy required to break bond is less than energy released when bonds formed, there is a release of energy (energy is a product in reaction)

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9
Q

What is an endothermic reaction?

A

Energy + A-B + C-D →A-D + C-B
If energy required to break bond is greater than energy released when bonds formed, need to be an external supply of energy

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10
Q

What is enthalpy?

A

Represents heat energy;

🔺H(reaction) = 🔺H(products) - 🔺H(reactants)

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11
Q

How can you define the signs of enthalpy?

A
  • If energy is released in a reaction = exothermic
    • sign of🔺H will be negative
  • If energy is absorbed in a reaction = endothermic
    • sign of 🔺H will be positive
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12
Q

Which reactions are spontaneous and nonspontaneous?

A
  • Most, but not all, exothermic reactions are spontaneous
  • Most, but not all, endothermic reactions are non-spontaneous
  • use entropy to determine*
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13
Q

What is the second law of thermodynamics?

A

Universe spontaneously tends toward increased disorder or randomness

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14
Q

What is entropy (s)?

A

Measure of randomness of chemical system

  • high entropy : highly disordered system (no order)
  • low entropy : well organized system like crystalline structure
  • negative entropy does not exist
  • g>l>s*
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15
Q

What is the formula for entropy?

A

🔺S(reaction) = S(products) - S(reactants)

  • positive 🔺S(reaction) = increased disorder for reaction (preferred)
  • negative 🔺S(reaction)=decreased order for reaction
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16
Q

How can entropy and the type of reaction affect spontaneity?

A
  • if exothermic & positive 🔺S → spontaneous
  • if endothermic & negative 🔺S → nonspontaneous
  • for any other situation, depends on relative size of 🔺H & 🔺S
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17
Q

What is free energy?

A

Represents combined contribution of enthalpy & entropy values for chemical reaction
🔺G=🔺H- T🔺S
- negative🔺G → always spontaneous
- positive 🔺G → never spontaneous

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18
Q

How do you determine free energy based on specific types?

A

🔺H+,🔺S- : 🔺G always +, regardless of T
🔺H-, 🔺S+ : 🔺G always -, regardless of T
🔺H+, 🔺S+ : 🔺G sign depends on T
🔺H-, 🔺S- : 🔺G sign depends on T

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19
Q

What is calorimetry?

A

Measurement of heat energy change in a reaction

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20
Q

What is calorimeter?

A

Device which measures heat changes in calories

- used to measure loss/gain of heat

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21
Q

How can you calculate gain/loss of heat energy?

A
  • exothermic: heat released by reaction is absorbed by surrounding solution
  • endothermic : reactants absorb heat from surrounding solution
22
Q

What is specific heat?

A

of calories of heat needed to increase temperature of 1 g of substance 1°C

23
Q

How do you determine heat (Q) released or absorbed?

A 
Q = m(s) x 🔺T(s) x SH(s)
-specific heat SH(s)
-mass of solution in grams (s)
- temperature change: final-initial (🔺T(s))
S= surrounding
24
Q

What is bomb calorimeter? Calorie?

A

Nutritional Calorie: (Cal): large “C” Calorie: 1kilocalorie: 1000 calories
Bomb Calorimeter: fuel value of food

25
What are kinetics?
Study of rate (or speed) of chemical reactions
26
What is an effective collision?
One that produces product molecules
27
What is activation energy?
(Ea) minimum amount of energy required to initiate chemical reaction
28
What is an activated complex?
Extremely unstable, short-lived intermediate complex - formation of this requires energy (Ea) to overcome energy barrier to start reaction - reactants → products via activated complex (can't be isolated from reaction mixture) - Ea: difference between energy of reactants & that of activated complex
29
What factors affect the reaction rate?
1. structure of reacting species 2. Molecular shape & orientation 3. Concentration of reactants 4. Temperature of reactants 5. Physical state of reactants 6. Presence of a catalyst
30
How does the structure of reacting species affect reaction rate?
- oppositely charged species react more rapidly - dissociate ions in solution whose bonds are already broken have very low activation energy - ions w/ same charge do not react - bond strength is important - covalent molecules bond must be broken w/ activation energy before new bonds can be formed - magnitude of activation energy related to bond strength
31
How does molecular shape and orientation affect reaction rate?
- Large molecules may obstruct reactive part of molecule - only molecular confessions with correct orientation lead to product formation - molecular collisions may or may not lead to chemical reaction
32
How aves concentration of reactions affect reaction rate?
- rate is related to concentration of for more reacting substances - rate will generally increase as concentration increases - more concentration → more reactant molecules per unit → more collisions per unit volume
33
How does temperature of recictunts affect reaction rate?
- rate increases as temperature increases - increase temperature relates directly to increase average kinetic energy - increase kinetic energy → increase speed of particles increase likelihood of collision (can lead to product formation)
34
How does the physical state of reactants affect reaction rate?
-reaction occurs when reactants can collide frequently with sufficient energy to react - solid states: atoms, ions, compounds close together but restricted in motion - gaseous state: particles are free to move but often far apart causing collision to be infrequent - liquid state: particles free to move and are in close proximity (Fastest) liquids > gas > solid (slowest)
35
How does the presence of a catalyst affect reaction rate?
- catalyst: substance that increases rate of reaction (by decreasing activation energy) - undergoes no net change - does not alter final product of reaction - interacts with reactants to create alternative pathway for product production - use of solid catalyst: Haber process: synthesis of ammonia facilitated by it
36
How do you find reaction rate?
- reaction rate is proportional to reactant concentration | Rate =k[reactant]
37
What is rate law?
- For reaction: A→ products - rate law: rate=k[A]^n - exponent in" is reaction order (determined experimentaly) - not same as coefficient of reactant - For reaction: A + B→ products - rate law: rate: K[A]^n [B]^n1
38
What is a reversible reaction?
Process that can occur in both directions (use equilibrium arrow symbol)
39
What is dynamic equilibrium?
Rate of forward process in reversible reaction is exactly balanced by rate of reverse process
40
What is a chemical equilibrium?
State of reaction in which rates for forward & reverse reactions are equal
41
What are equilibrium reactions?
Chemical reactions that do not go to completion ( aka incomplete reactions)
42
What is completion?
All reactants have been converted to products
43
What is equilibrium?
Reactant depletion= product depletion | - forward & reverse reactions are equal
44
What is the generalized equilibrium expression for a chemical reaction?
aA+bB → cC+dD - A&B= reactants, C&D = products, a, b,c,d= coefficients of balanced equation K(eq)= ([C]^c[D]^d)/([A]^a[B]^b)
45
How do you write an equilibrium constant expression?
- equilibrium constant expression only be written after balanced equation - each chemical equation has unique equilibrium constant value at specific temperature - brackets represent molar concentration [M] - all equilibrium constants shown as unit less - only concentration of gases & substances in solutions shown
46
How do you interpret equilibrium constants?
1. K(eq)> 1x10^3 - large value of Keq indicates numerator (product) >>> denominator (reactant) - equilibrium mostly product present 2. K(eq) < 1x10^-3 - small value of Keq indicates numerator (product) <<< denominator (reactant) - equilibrium mostly reactant present 3. k(eq) btwn 1x10^-3 and 1x10^3 - equilibrium mixture contains significant concentrations of both reactants and products
47
How do you calculate equilibrium constants?
- reversible reaction is allowed to proceed until system reaches equilibrium - amount of reactants & products no longer changes
48
What is lechatelier's principle?
If a stress is placed on system at equilibrium, system will respond by altering equilibrium composition in such a way as to minimize stress - product introduced: reaction shifts left - reactant introduced reaction shifts right
49
What is the effect of concentration on equilibrium?
- Add or subtract either reactants or products at fixed volume = concentration change - remove material to decrease concentration - system react to stress to return concentrations to appropriate ratio
50
What is the effect of heat on equilibrium?
- exothermic reaction: treats heat as product - addition of heat = increase amount of product - increase product shifts equilibrium to left(more amount of reactants & decrease amount of product - endothermic reaction: treat heat as reactant - reaction will shift right if heat is added by increase in temperature
51
What the effect of pressure on equilibrium?
- pressure affects equilibrium only if one or more substances in reactions are gases - relative # of gas moles on reactant & product side must differ - when pressure increases → shift to side with less moles of gas - when pressure decreases → sniff to side with more moles of gas
52
What is the effect of a catalyst on equilibrium?
- Has no effect on equilibrium - increase rate of both forward & reverse reaction to same extent - while equilibrium & concentration not change → equilibrium reached in shorter time

Chemistry 101 (4 decks)

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