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reactivity 2 Flashcards

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1
Q

What is a chemical equation?

A

shows the ratio of products and reactants that can be written as a chemical or symbol equation

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2
Q

What are stoichometric coefficients?

A

numbers in front of products and reactants used to balance the equations

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3
Q

What can a mole ratio determine?

A
  1. the mass or volumes of reactants and products
  2. concentration of products and reactants in a solution
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4
Q

What is Avogadro’s Law?

A

equal volumes of all gases under STP contain equal number of moles

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5
Q

What is molar volume?

A

volume occupied by 1 mole of a gas

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6
Q

How is titration carried out?

A
  1. use a pipette to measure a known volume of one solution into a conical flask with universal indicator
  2. put the other solution in a burette, which is a calibrated glass tube
  3. open the burette to allow the solution into the conical flask and mix it
  4. add indicator and keep mixing until there is a permanent color change
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7
Q

How is back titration carried out?

A
  1. known excess of one of the reactants is added to the reaction mixture
  2. unreacted excess is determined by titration of a standard solution
  3. subtract the unreacted amount from the original to work out the reacting amount
    - used when the end point is hard to identify for impure substances
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8
Q

What assumptions are made during a back titration?

A
  1. all NaHCO3 reacts with the acid
  2. only NaHCO3 reacted with the HCl from the tablet
  3. took place under standard conditions
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9
Q

What is the limiting reactant?

A

reactant that gets used up in a reaction and determines the theoretical yield of a product

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10
Q

What is the difference between theoretical and experimental yield?

A

theoretical - maximum amount of product obtained if 100% of the limiting reactants is converted into product
experimental - yield that is actually produced

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11
Q

How do you work out % yield?

A

(experimental yield / theoretical yield) x 100

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12
Q

What can cause EY to be lower than TY?

A
  • side reactions
  • decomposition of reactants or products
  • product lost during purifying
  • reversible chemical reaction
  • incomplete reaction
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13
Q

What can cause TY to be lower than EY?

A
  • impurities in a product
  • product not fully dried
  • incomplete reaction
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14
Q

How do you work out atom economy?

A

(Mr of desired product / Mr of sum of reactants) x 100

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15
Q

What is green chemistry?

A

sustainable design of chemical products and processes
- aims to minimize use and generation of substances that are hazardous to human health and the environment

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16
Q

What is dynamic equilibrium?

A

rate of forward reaction is equal to the rate of the backward reaction in a closed system where concentration of products and reactants are equal

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17
Q

What happens when Br2 is stored in a sealed container at STP in a physical system?

A

as Br2 is volatile and has a boiling point close to STP, most molecules will evaporate but as it is a sealed container, concentration increases and some molecules collide with the walls of the container, losing energy and changing state

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18
Q

When is there equilibrium in a physical system?

A

rate of evaporation = rate of condensation
- rate doesn’t stop, but just become equal
- crystals may also change shape

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19
Q

What happens when you place HI in a sealed container?

A

starts off colorless, becomes more and more purple until concentration and color remain constant
2HI (g) colourless ⇌ H2 (g) colourless + I2 (g) purple

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20
Q

What does RECCCS stand for?

A

Rates
Equal
Concentration
Constant
Closed
System

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21
Q

What are the 5 characteristics of an equilibrium state?

A

1.equilibrium is dynamic - occur at the same rate meaning that the reaction doesn’t stop
2.equilibrium is achieved in a closed system - no exchange of matter, so there is equilibrium when the products and reactants recombine with each other
3. concentration of products and reactants remain constant at equilibrium - being produced and destroyed at the same rate
4. no change in macroscopic properties at equilibrium - observable properties are dependent on concentration
5.equilibrium can be reached in either direction for reversible reactions

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22
Q

What is the equilibrium position?

A

measure of the proportion of product to reactant

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23
Q

What is the equilibrium law?

A

describes how the equilibrium constant K can be determined from stoichometry of a reaction

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24
Q

What is the equilibrium constant?

A

magnitude of the equilibrium constant indicates the extent of a rate of reaction at equilibrium - it is temperature dependent
0 - mostly reactants
1 - mostly products

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25
Q

How do you calculate the equilibrium constant?

A

K = (concentration of products to the power of co-efficient) / (concentration of reactants to the power of co-efficient)

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26
Q

What does the magnitude of K tell us?

A

K ≤ 1 - reaction hardly proceeds
K < 1 - equilibrium lies towards the reactants
K= 1 - significant amounts of both products and reactants
K > 1 - equilibrium lies towards the products
K ≥ 1 - reaction almost goes to completion

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27
Q

How do you work out K for the reverse reaction?

A

find the reciprocal

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28
Q

What is Le Chatelier’s Principle?

A

a system at equilibrium when subject to a change will respond in such a way to minimize the effects of the change

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29
Q

What happens to equilibrium if concentration changes?

A

increase in reactant / decrease in product concentration - right
decrease in reactant / increase in product concentration - left
- doesn’t affect k, but will affect position of equilibrium

30
Q

What happens to equilibrium if pressure changes?

A

increase pressure - moves to the side with the fewest amount of particles
decrease pressure - moves to the side with the most amount of particles
- doesn’t affect k, but will affect position of equilibrium

31
Q

What happens to equilibrium if temperature changes?

A

increase temperature - endothermic direction (increase value of k)
decrease temperature - exothermic direction (decrease value of k)

32
Q

What happens to equilibrium if a catalyst is added?

A

speeds up the rate of reaction in both directions and doesn’t affect k or the position of equilibrium
- enable the equilibrium mixture to be achieved more quickly, but doesn’t change yield of a single reaction

33
Q

What is the Haber Process?

A

N2 (g) + 3H2 (g) ⇌ 2NH3 (g) H = -93kjmol-1

34
Q

Why is the Haber Process important?

A

important for the production of fertilizers to increase yield of food production

35
Q

What are the conditions of the Haber Process?

A

high pressure (200atm), compromised temperature (450), iron based catalyst, decreased product and increased reactant concentration

36
Q

What is the contact process?

A

2SO2 (g) + O2 (g) ⇌ 2SO3 (g) H=-198kjmol-1

37
Q

Why is the contact process important?

A

important for the production of sulfuric acid for fertilizers, water treatment, steel and a measure of a countries industrial strength

38
Q

What are the conditions of the contact process?

A

200 atm, 450 degrees, V2O5 catalyst

39
Q

What is the methanol production process?

A

CO (g) + 2H2 (g) ⇌ CH3OH (g) H=-90kjmol-1

40
Q

Why is the methanol production process important?

A

used for chemical feedstocks, solvents and biofuels

41
Q

What are the conditions for the production of methanol?

A

high pressure, moderate temperature that is a compromise between yield and rate

42
Q

What is a rate?

A

reciprocal value of time and has the units of s-1

43
Q

What is a rate of reaction?

A

change in concentration of a product or reactant over time
- increase in concentration of products
- decrease in concentration of reactants
- measured in mol dm-3 s-1

44
Q

What is a tangent?

A

straight line with the same gradient as the point it touches on the graph

45
Q

How do you calculate rate of reactions?

A
  1. increase in product concentration / time
  2. decrease in reactant concentration / time
46
Q

What are the 6 methods of measuring rates of reactions?

A
  1. change in volume
  2. change in mass
  3. intensity of a specific wavelength of light being absorbed is changing
  4. change in concentration measured using titration (quenching)
  5. change in concentration using conductivity
  6. clock reaction - disappearing cross
47
Q

Change in volume: what is the equipment, process and units?

A

process - a gas is being produced
equipment - gas syringe or upturned burette (insoluble gases)
units - cm3 s-1

48
Q

Change in mass: what is the equipment, process and units?

A

process - heavy gas is being produced
equipment - balance
units - g s-1

49
Q

Intensity of a specific wavelength of light being absorbed is changing: what is the equipment, process and units?

A

process - need to calibrate and know which wavelength is needed
equipment - colorimeter
units -mol dm-3 s-1

50
Q

Change in concentration measured using titration: what is the equipment, process and units?

A

process - iodine/H+/OH- are being produced or used up
equipment - burette
units - mol dm-3 s-1

51
Q

Change in concentration using conductivity: what is the equipment, process and units?

A

process - concentration of ions are changing
equipment - conductivity probe connected to a datalogger
units - mol dm-3 s-1

52
Q

Clock reaction: what is the equipment, process and units?

A

process - sudden change in colour
equipment - timer
units - s-1 which can be converted to mol dm-3 s-1

53
Q

heat

A

sum of energy of all particles

54
Q

what happens when you move between states?

A

as you move from solid to liquid to gas, particles gain kinetic energy due to an increase in temperature

55
Q

What does the Maxwell-Boltzmann curve show?

A

shows the number of particles having a specific value of kinetic energy against the values of kinetic energy

56
Q

What does the Maxwell-Boltzmann curve tell us about distribution?

A
  • large number of molecules with less energy
  • small number of molecules with more energy
57
Q

What is required for a reaction to occur?

A
  • enough energy
  • correct orientation
58
Q

What is activation energy?

A

minimum value of kinetic energy which particles must have so that they can react
- energy is required so that the transition state between reactants and products can occur

59
Q

What 5 factors affect the rate of reaction?

A
  • temperature
  • pressure
  • surface area
  • concentration
  • catalyst
60
Q

How can temperature affect the rate of reaction?

A

as temperature increases, the number of molecules that have significant activation energy increases (area under the line to the right increases) and so does kinetic energy
- collision frequency also increases as the particles will be moving faster so there will be more successful collisions

61
Q

How can temperature affect the Maxwell-Boltzmann curve?

A
  • peak shifts to the right
  • peak is broader
  • peak is lower
  • same area under the curve
  • majority of particles have a higher energy
62
Q

How can concentration affect the rate of reaction?

A

increasing concentration increases the rate as the particles are closer together (more particles per cm3) and so frequency of successful collisions increases
- as the reaction proceeds, the rate slows down as concentration drops when all the reactants are used up

63
Q

How can concentration change be seen in a graph?

A

if there is a lower concentration:
- less product is made so lower plateau
- less steep gradient

64
Q

How can pressure affect the rate of reaction?

A

particles are closer together as pressure increases due to less space in the container, so the frequency of successful collisions increase as well as the rate of reaction
- only occurs in gases

65
Q

How can pressure change be seen on a graph?

A
  • same amount of product made
  • less steep for a lower pressure
66
Q

How can surface area affect the rate of reaction?

A

smaller solids –> surface area increases
- this means that there is a larger surface area for particles to collide on, increasing the chance of successful collisions and the rate of reaction

67
Q

How can surface area change be seen in a graph?

A
  • same amount of product made
  • larger solids have a less steep gradient
68
Q

How can catalysts affect the rate of reaction?

A

catalysts increase the rate of reaction without being used up by providing an alternate reaction pathway with a lower activation energy, causing the frequency of successful collisions to increase and the rate as more collisions occur with greater than minimum energy required to overcome the activation energy barrier
e.g) enzymes in the body of transition metals in chemical reactions

69
Q

How can catalysts be seen on the Maxwell-Boltzmann curve?

A

shifts the activation energy line to the left so more particles have energy to react

70
Q

What are systematic errors?

A

when all measurements are higher or lower than the expected value

71
Q

What are random errors?

A

errors occur in individual measurements due to equipment, changes in surrounding, misinterpreted measurements or insufficient number of trials

chemistry (28 decks)

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