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Higher Chemistry > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

How do you calculate the mass of a substance?

A

M = n x G

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2
Q

How do you calculate the number of moles?

A 
n = M / G   
or  
n = C x V 
or
n = Vg / Vm
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3
Q

How do you calculate the volume of solution in Litres?

A

V = N / C

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4
Q

How to calculate percentage yield:

A

Actual yield
————————- x 100
theoretical yield

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5
Q

How to calculate atom economy:

A

mass of desired product(s)
—————————————– x 100
total mass of reactants

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6
Q

How do you calculate energy required to heat water? (Eh)

A

Eh = c x m x ΔT

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7
Q

What does C stand for? (in “Eh = c x m x ΔT” equation)

A

specific heat capacity of water; 4.18

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8
Q

What does M stand for? (in “Eh = c x m x ΔT” equation)

A

mass of water heated in kg

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9
Q

What does ΔT stand for?

A

temperature change of the water

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10
Q

What is enthalpy of combustion?

A

the enthalpy change when 1 mole of a substance burns completely in oxygen

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11
Q

What does it mean when ΔH is negative?

A

an Exothermic reaction has occurred; energy is lost during the reaction

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12
Q

What does it mean when ΔH is positive?

A

an endothermic reaction has occurred, energy is absorbed during the reaction

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13
Q

combustion reactions are always what?

A

exothermic

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14
Q

What are the reasons why all the heat released by burning an alcohol was not taken up by water? (3)

A
  • the container and the surrounding became hot
  • water lost heat to the surroundings
  • the ethanol did not burn completely
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15
Q

When an ionic substance is dissolved in water, two processes occur which include:

A
  • the ionic lattice gets broken apart-this requires energy- endothermic
  • water molecules bond to the ions due to the polarity of water molecules - this releases energy - exothermic
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16
Q

What is enthalpy of solution? ΔHsoln

A

the enthalpy change that occurs when 1 mole of a substance dissolves completely in water

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17
Q

What is enthalpy of neutralisation? ΔHneut

A

the enthalpy change per mole of water when an acid is neutralised by an alkali

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18
Q

What does the enthalpy change for a reaction depend on?

A

quantity of reactants and products

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19
Q

What is Hess’s law?

A

the overall enthalpy change in a reaction, or sequences of reactions, depends only on the reactants and products and not on the route taken

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20
Q

What is the equation for Hess’s law?

A

ΔH1 = ΔH2a + ΔH2b

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21
Q

What happens to energy when free atoms form covalent bonds? and what is this called?

A 
energy is released 
Bond enthalpy (energy)
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22
Q

What is bond dissociation enthalpy?

A

when the same quantity of energy has to be input to break the covalent bond in a mole of H2 molecules to produce 2 moles of free hydrogen atoms
- reverse reaction (endothermic)

23
Q

What is mean bond enthalpy?

A

when considering the energy associated with a covalent bond in compound

24
Q

What is bond enthalpy?

A

the energy released (exothermic) when one mole of covalent bonds if formed from free atoms in the gaseous state

25
Q

What is oxidation?

A

gain of oxygen or loss of electrons

26
Q

What is reduction?

A

loss of oxygen or gain of electrons

27
Q

What is a redox reaction?

A

when a reduction and oxidation reaction always takes place together as electrons transfer from one reactant to the other

28
Q

What is an oxidising agent?

A

a chemical which acts on another substance to oxidise it. an oxidising agent is reduced during the reaction

29
Q

What is a reducing agent?

A

a chemical which acts on another substance to reduce it. a reducing agent is oxidised during the reaction

30
Q

In the electrochemical series, what letter (shape) is shown when forming a redox reaction?

A

“z”

31
Q

In the electrochemical series, what happens to the higher reaction?

A

it is written in reverse and is oxidised

  • oxidation reaction
  • reducing agent (electron donor)
32
Q

In the electrochemical series, what happens to the lower reaction?

A

Its written the same way as the book and is reduced

  • reduction reaction
  • oxidising agent (electron acceptor)
33
Q

What does electron transfer involve? and when does it take place?

A

has to involve one substance donating electrons and another substance accepting electrons, it takes place during a redox reaction

34
Q

In a redox reaction, what is a reducing agent described as??

A

the electron donor

35
Q

In a redox reaction, what is an oxidising agent described as?

A

electron acceptor

36
Q

Which group are described as strong oxidising agents (electron acceptors)?

A

the halogens

37
Q

Before two ion-electron half equations can be combined, which two conditions must be met?

A
  • one equation must be for an oxidation change and the other must be for a reduction change
  • the number of electrons in each equation must be made the same
38
Q

What are the 4 steps (in order) for creating an ion-electron equation from scratch?

A

step 1 - balance the non-oxygen symbols
step 2 - balance the oxygen by adding water (H20)
step 3 - balance the hydrogen by adding H+
step 4 - balance the charges by introducing electrons

39
Q

What is a standard solution?

A

a solution of accurately known concentration

40
Q

What does ⇄ mean?

A

the reaction can go in either reaction

41
Q

What does chemical equilibrium involve?

A

two-way reactions known as reversible reactions

42
Q

What is chemical equilibrium?

A

eventually the rate of the backward reaction will equal the rate of the forward reaction. from then on the concentration of all substances in the reaction remain constant

43
Q

What is chemical equilibrium described as?

A

dynamic equilibrium

44
Q

What happens to the position of equilibrium if the equilibrium mixture contains a greater proportion of products than reactants?

A

lies to the right

45
Q

What happens to the position of equilibrium if the equilibrium mixture contains a greater proportion of reactants than products?

A

lies to the left

46
Q

What is a closed system?

A

when a reaction is carried out in a sealed container to prevent any loss of chemicals, or addition of chemicals to the reaction

47
Q

What is dissociation or ionisation of water?

A

when the position of the equilibrium lies well to the left, it is 99.9999% covalent and only contains a trace amount of ions

48
Q

What are the rates of most chemical reactions altered by?

A
  • changing the concentration
  • increasing the temperature
  • adding a catalyst
  • altering the pressure
49
Q

What is stated in Le Chatelier’s principle?

A

an equilibrium system always changes to reduce the effect of any outside change made on it

50
Q

What effect on equilibrium mixture does increasing the concentration of any reactant have?

A

it increases the concentration of the products

51
Q

What effect on equilibrium mixture does increasing the temperature have?

A

it shifts the position of equilibrium in the endothermic direction

52
Q

What effect on equilibrium mixture does increasing the pressure have?

A

it shifts the position of equilibrium in the direction of smaller gas volumes

53
Q

What effect on equilibrium mixture does adding a catalyst have?

A

it has no effect on the equilibrium position but allows it to be reached faster

Higher Chemistry (3 decks)

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