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Chemistry OCR A-Level > Topic 3 > Flashcards

Topic 3 Flashcards

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1
Q

define standard enthalpy change of reaction

A

the enthalpy change that accompanies a reaction under standard conditions and all reactants and products are in standard state

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2
Q

define standard enthalpy change of formation

A

the enthalpy change when 1 mole of a compound is formed from its constituent elements under standard conditions when all reactants and products are in standard state

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3
Q

define standard enthalpy change of combustion

A

the enthalpy change when 1 mol of a substance completely reacts with oxygen under standard conditions and all reactants and products are in standard state

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4
Q

define exothermic

A

heat energy is lost to the surroundings. the energy released from bond formation is greater than the energy absorbed breaking the original bonds

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5
Q

define endothermic

A

heat energy is absorbed
the energy absorbed breaking the original bonds is greater than energy released forming new bonds

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6
Q

define activation energy and what way does the arrow face on an energy profile

A

the minimum energy required for a chemical reaction to take place
always up

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7
Q

what are standard conditions and standard state

A

298K and 1 atm and 1 moldm^-3
the physical state of elements under standard conditions

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8
Q

define enthalpy

A

heat content stored in a chemical system

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9
Q

define enthalpy change

A

the heat exchanged with the surroundings during a chemical reaction
the difference between the enthalpy of the products and the reactants

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10
Q

what is the equation for energy change

A

Q = MCΔT

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11
Q

how do you work out enthalpy change from energy change

A

ΔH = Q/n

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12
Q

define enthalpy change of neutralisation

A

the enthalpy change when 1 mol of water is formed from a neutralisation reaction under standard conditions and all reactants and products are in standard state

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13
Q

what are the causes for less energy bring transferred than expected when working out enthalpy change of combustion

A

heat loss to surroundings
incomplete combustion
evaporation
non-standard conditions

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14
Q

what is the value of enthalpy change of neutralisation

A

-57.5kJmol

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15
Q

define average bond enthalpy

A

energy required to break 1 mol of a specified type of bond in a gaseous molecule

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16
Q

what are the properties of bond enthalpy

A

energy is always required to break bonds]always positive and always have a positive enthalpy value

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17
Q

what kind of energy and enthalpy change are bond formation

A

exothermic and releases energy

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18
Q

what is Hess’s Law

A

If a reaction can take place by more than one route, the initial and final concentrations are the same and the total energy change is the same for each route

19
Q

what is reaction rate

A

the change in concentration of a reactant/product in a given time

20
Q

what makes an effective collision

A

sufficient speed and correct orientation

21
Q

whta factors can change rate of a chemical reaction

A

concentration
temperature
pressure
use of a catalyst
surface area of solid reactants

22
Q

what effect does increasing pressure have on reactants and why

A

increases rate
particles have more energy so there are more frequent successful collisions and therefore an increased rate

23
Q

what is the rule of thumb for reaction rate and temperature

A

a 10 degree increase in temperature doubles the rate

24
Q

what effect does increasing concentration/pressure have on rate of reaction

A

increases rate as there are more particles per unit of volume which leads to more successful and frequent collisions and therefore an increased rate

25
Q

how can progress of a chemical reaction be followed

A

monitoring removal of a reactant/formation of a product

26
Q

what 2 ways are there to determine rate of reaction when gas is produced

A

monitoring volume of gas produced or loss of mass of reactants

27
Q

what does a catalyst do

A

increase rate of reaction by lowering activation energy by offering a lower reaction pathway leading to more particles exceeding activation energy
is not used up in the reaction/is regenerated at the end

28
Q

what is a homogenous catalyst

A

catalyst that is in the same state as the reactants

29
Q

how does a homogenous catalyst interact with reactants

A

forms an intermediate which breaks down to give the product and regenerates the catalyst

30
Q

give 2 examples of homogenous catalysts

A

sulfuric acid - production of esters
chlorine radicals in zone repletion

31
Q

what is different about the equilibrium constant to regular constants

A

only constant at a given temperature

32
Q

how does a Boltzmann distribution model show the effects of a catalyst

A

Ea is lower than normal so a greater proportion of particles exceed the lower Ea

33
Q

what is Le Chatelier’s principle

A

when a system in dynamic equilibrium experiences an external change, equilibrium will shift to minimise the effect

34
Q

does a catalyst have an effect on equilibrium

A

no

35
Q

How is Kc worked out in aA + bB -> cC + dD

A

[C]c x [D]d / [A]a x [B]b

36
Q

what is an autocatalysis

A

a reaction product that acts as a catalyst for that reaction

37
Q

what are the main features of a Boltzmann Distribution model

A

no molecules have 0 energy
no maximum energy
area under curved is equal to the number of molecules/particles

38
Q

how does a Boltzmann Distribution curve change when temperature increases

A

peak is lower and shifted to the right, a greater proportion of molecules can exceed Ea

39
Q

what are the main properties of a catalyst

A

not used up in a reaction
regenerated at the end of a reaction
may react with reactant to form an intermediate and provide a surface for the reaction to take place on

40
Q

what is dynamic equilibrium

A

when the rate of the forwards reaction equals the rate of the backwards reaction at the same time in a closed system where the concentration of reactants and products remain constants

41
Q

what are the benefits of using a catalyst

A

lowers Ea
less electricity is used
product is made faster and cuts costs and increases profits

42
Q

what is a heterogenous catalyst

A

a catalyst that is in a different state to the reactants

43
Q

how does a heterogenous catalyst interact with reactants

A

usually solids in contact with gaseous reactants / reactants in solution
reactants are adsorbed onto the surface where the reaction takes place
after the reaction, products leave via desorption

44
Q

give examples of a heterogenous catalyst

A

iron in the haber process
nickel - hydrogenation of alkenes

Chemistry OCR A-Level (2 decks)

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