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Chemistry 101 > Energy, Rate, & Equilibrium > Flashcards

Energy, Rate, & Equilibrium Flashcards

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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
Q

What are kinetics?

A

Study of rate (or speed) of chemical reactions

26
Q

What is an effective collision?

A

One that produces product molecules

27
Q

What is activation energy?

A

(Ea) minimum amount of energy required to initiate chemical reaction

28
Q

What is an activated complex?

A

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
Q

What factors affect the reaction rate?

A
  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
Q

How does the structure of reacting species affect reaction rate?

A
  • 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
Q

How does molecular shape and orientation affect reaction rate?

A
  • 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
Q

How aves concentration of reactions affect reaction rate?

A
  • 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
Q

How does temperature of recictunts affect reaction rate?

A
  • 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
Q

How does the physical state of reactants affect reaction rate?

A

-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
Q

How does the presence of a catalyst affect reaction rate?

A
  • 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
Q

How do you find reaction rate?

A
  • reaction rate is proportional to reactant concentration

Rate =k[reactant]

37
Q

What is rate law?

A
  • 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
Q

What is a reversible reaction?

A

Process that can occur in both directions (use equilibrium arrow symbol)

39
Q

What is dynamic equilibrium?

A

Rate of forward process in reversible reaction is exactly balanced by rate of reverse process

40
Q

What is a chemical equilibrium?

A

State of reaction in which rates for forward & reverse reactions are equal

41
Q

What are equilibrium reactions?

A

Chemical reactions that do not go to completion ( aka incomplete reactions)

42
Q

What is completion?

A

All reactants have been converted to products

43
Q

What is equilibrium?

A

Reactant depletion= product depletion

- forward & reverse reactions are equal

44
Q

What is the generalized equilibrium expression for a chemical reaction?

A

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
Q

How do you write an equilibrium constant expression?

A
  • 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
Q

How do you interpret equilibrium constants?

A
  1. K(eq)> 1x10^3
    • large value of Keq indicates numerator (product)&raquo_space;> 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
Q

How do you calculate equilibrium constants?

A
  • reversible reaction is allowed to proceed until system reaches equilibrium
  • amount of reactants & products no longer changes
48
Q

What is lechatelier’s principle?

A

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
Q

What is the effect of concentration on equilibrium?

A
  • 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
Q

What is the effect of heat on equilibrium?

A
  • 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
Q

What the effect of pressure on equilibrium?

A
  • 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
Q

What is the effect of a catalyst on equilibrium?

A
  • 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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