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chemistry > C3 - chemical reactions (from PMT) > Flashcards

C3 - chemical reactions (from PMT) Flashcards

1
Q

define an ionic equation

A

an equation that only shows the ions which take part in a reaction. it can be written for any reaction involving ions in solution.

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2
Q

define the mole

A

one moles is the amount of a substance containing the same number of particles as there are atoms in exactly 12.0g of carbon-12. this is 6.02*10^23

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3
Q

what is the avogadro constant?

A

the number of atoms, molecules or ions in one mole of a given substance. this has a value of 6.02*10^23

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4
Q

what equation links the avogadro constant to number of moles?

A

number of particles = moles * avogadro constant

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5
Q

what equation links mass, number of moles and relative atomic mass?

A

mass(g) = moles x relative atomic mass (Mr)

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6
Q

what is a limiting reagent?

A

-in a reaction between two substances, one reactant will often be used in excess to ensure that all of the other reactant is used up
-the reactant which isn’t in excess is the limiting reagent as it limits the amount of product that can be formed

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7
Q

give an example of a type of reaction that is exothermic?

A

-combustion
-neutralisation

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8
Q

give an example of an endothermic reaction

A

-thermal decomposition
-photosynthesis

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9
Q

what is a reaction profile?

A

-a graph that shows the activation energy of a reaction with the relative energies of the reactants and products

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10
Q

what is needed for a reaction to occur?

A

reactant particles need to collide at the correct orientation with sufficient energy

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11
Q

what is the activation energy of a reaction?

A

the minimum amount of energy required for a reaction to occur

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12
Q

in terms of bond energies, what happens in a chemical reaction? describe exothermic and endothermic reactions in terms of bonds breaking/forming

A

-energy is needed to break bonds
-exothermic: energy used to break bonds is greater than the energy released when making bonds
-endothermic: energy released when forming bonds is greater than the energy used to break bonds

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13
Q

how can the energy change of a reaction be calculated using bond energies?

A

energy of reaction = total energy of bonds broken - total energy of bonds made

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14
Q

what is a neutralisation reaction?

A

a reaction between an acid and an alkali or base, forming a salt and water

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15
Q

what is formed when an acid dissolves in water?

A

hydrogen ions

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16
Q

what is formed when an alkali dissolves in water?

A

hydroxide ions

17
Q

what is produced when an acid reacts with a metal carbonate?

A

-salt
-water
-carbon dioxide

18
Q

what is produced when an acid reacts with a metal?

A

-salt
-hydrogen

19
Q

what is the difference between a strong and weak acid?

A

-the strength of the acid refers to the degree of ionisation
-strong acids are completely ionised in an aqueous solution (lots of H+ ions released)
-weak acids are only partially ionised in an aqueous solution (fewer H+ ions released)

20
Q

give examples of strong and weak acids

A

strong: hydrochloric, sulfuric
weak: ethanoic

21
Q

what do the terms dilute and concentrated mean?

A

concentration refers to the amount of substance in a given volume of solution

a dilute solution is one where a small amount of solute has been added to a given volume of solvent. in a concentrated solution, a large amount of solute has been added

22
Q

in terms of acids, what is the difference between the terms strong/weak and dilute/concentrated?

A

-strong/weak refers to the degree of ionisation of the acid
-dilute/concentrated refers to the amount of substance in a given amount of solution

23
Q

which pH values describe an acid, alkali and neutral solution?

A

acid: pH <7
neutral: pH=7
alkali: pH>7

24
Q

as the pH decreases by one unit, what happens to the concentration of H+ ions?

A

increases by a factor of 10

25
Q

describe the concentration of H+ ions and pH of a strong acid

A

-high concentration of H+ ions
-pH value close to 0, within the range 0-7

26
Q

what colour is phenolphthalein in acid and alkali?

A

acid - colourless
alkali - pink

27
Q

what colour is methyl orange in acid and alkali?

A

acid - red
alkali - yellow

28
Q

what happens to blue litmus paper in acid and alkali?

A

acid - turns red
alkali - stays blue

29
Q

what happens to red litmus paper in acid and alkali?

A

acid - stays red
alkali - turns blue

30
Q

what is the problem with using universal indicator to test the pH of a solution?

A

-colour of the solution is to be matched to a pH colour chart which is quite subjective (people may disagree upon the exact colour of the solution)
-does not provide an exact pH value

31
Q

what is electrolysis?

A

a process which uses electrical energy to decompose electrolytes

32
Q

what are cations and anions?

A

cations: positive ions
anions: negative ions

33
Q

what is the cathode and anode?

A

cathode: negative electrode
anode: positive electrode

34
Q

during electrolysis what forms at the cathode and anode?

A

cathode: metal /hydrogen
anode: non-metal

35
Q

what happens at the anode during electrolysis?

A

the negatively charged ions are attracted to the anode where they lose electrons to form their elements

36
Q

what happens at the cathode during electrolysis?

A

the positively charged ions are attracted to the cathode where they gain electrons to form their elements

37
Q

name the process that occurs at each electrode

A

anode: oxidation
cathode: reduction

38
Q

why are inert electrodes often used during electrolysis?

A

when the products are very reactive to prevent any further reactions occurring

39
Q

give an example of when non-inert electrodes are used during electrolysis

A

-purification of impure copper using copper sulfate solution
-one electrode must be the impure copper (which takes part in the reaction) rather than an inert electrode

chemistry (8 decks)

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