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advanced information paper 1 Flashcards

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1
Q

what are the properties of ionic compounds?

A

they all have high melting and boiling points due to the many strong bonds between the ions.

When they’re solid, the ions are held in place, so the compounds can’t conduct electricity, however when they melt the ions are free to move and they’ll carry electric current.

some ionic compounds dissolve in water. The ions separate and are all free to move in the solution, so they’ll carry electric current

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2
Q

what makes covalent bonds very strong?

A

the positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces

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3
Q

what are the properties of simple molecular structures?

A
  • held together with strong covalent bonds
  • weak intermolecular forces
  • low melting and boiling point - most molecular substances are gases or liquids at room temperature
  • don’t conduct electricity
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4
Q

as molecules get bigger, does the strength of the intermolecular forces increase or decrease? Do the melting and boiling points increase or decrease?

A

increase, increase

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5
Q

what are three structures that have covalent bonds?

A

simple molecular substances, polymers and giant covalent substances

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6
Q

what are polymers?

A

long chains of repeating units

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7
Q

what do you do instead of drawing out a whole long polymer molecule, which can contain thousands or even millions of atoms?

A

you can draw the shortest repeating section (repeating unit)

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8
Q

how do you find the molecular formula of a polymer?

A

write down the formula of the repeating unit in brackets and put an ‘n’ outside

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9
Q

are the intermolecular forces between polymer molecules smaller or larger than between simple molecular substances?

A

larger

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10
Q

what state are most polymers at room temperature?

A

solid

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11
Q

are the intermolecular forces between polymer molecules stronger or weaker than ionic and covalent bonds?

A

weaker

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12
Q

are giant covalent structures macromolecules or micromolecules?

A

macromolecules

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13
Q

what are some properties of giant covalent structures?

A
  • very high melting and boiling points as a lot of energy is needed to break the strong covalent bonds
  • they don’t contain charged particles so they don’t conduct electricity, even when molten (with some exceptions)
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14
Q

what are three examples of giant covalent structures?

A

Diamond, graphite and silicon dioxide

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15
Q

describe the structure of diamond

A

each carbon atom forms 4 covalent bonds in a very rigid giant covalent structure

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16
Q

describe the structure of graphite

A

each carbon atom forms 3 covalent bonds to create layers of hexagons. Each carbon atom also has one delocalised electron

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17
Q

what does silicon dioxide (sometimes called silica) make up?

A

sand. Each grain of sand is one giant structure of silicon and oxygen.

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18
Q

name 4 allotropes of carbon

A

diamond, graphite, graphene and fullerenes

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19
Q

are there covalent bonds between the layers of graphite? What does this mean?

A

there are no covalent bonds between the layers of carbon, which means that they’re only held together weakly so they’re free to move over each other. This makes graphite soft and slippery, so it’s ideal as a lubricating material

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20
Q

can graphite conduct heat and electricity? why?

A

graphite can conduct heat and electricity because each carbon atom only makes three bonds, which leaves one delocalised electron for each carbon atom. These are free to move throughout the structure and so can conduct heat and electricity.

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21
Q

what is graphene?

A

one layer of graphite

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22
Q

what are the properties of graphene?

A
  • the network of covalent bonds makes it very strong
  • it’s light, so it can be added to composite materials to improve their strength without adding too much weight
  • it contains delocalised electrons which means it can conduct electricity
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23
Q

what are the properties of nanotubes?

A
  • can conduct both electricity and thermal energy
  • have a high tensile strength (don’t break when they are stretched)
  • nanotubes can be used in electronics or to strengthen materials without adding much weight, such as in tennis racket frames
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24
Q

what is responsible for producing all the properties of metals?

A

the delocalised electrons

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25
Q

what are the properties of metallic bonds?

A
  • very strong
  • solid at room temperature (except mercury)
  • good conductors of electricity and heat
  • most metals are malleable
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26
Q

why are most metals solid at room temperature?

A

the electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong, so a lot of energy needs to be overcome in order to melt them.

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27
Q

why are metals good conductors of electricity and heat?

A

the delocalised electrons can carry electrical current and thermal energy through the whole structure

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28
Q

why are most metals malleable?

A

the layers of atoms in a metal can slide over each other, making metals malleable - this means that they can be bent or hammered or rolled into flat sheets

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29
Q

what is harder, alloys or pure metals?

A

alloys

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30
Q

what is an alloy?

A

a mixture of two or more metals or a metal and another element

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31
Q

why are alloys harder than pure metals?

A

different elements have different sized atoms, so when another element is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other, making alloys harder than pure metals

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32
Q

what are the three states of matter?

A

solid, liquid, gas

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33
Q

what does which state a substance is at at a certain temperature depend on?

A

how strong the forces of attraction are between the particles of the material

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34
Q

what three things does the strength of the forces of attraction between the particles depend on?

A
  1. the material (the structure of the substance and the type of bonds holding the particles together)
  2. the temperature
  3. the pressure
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35
Q

what is particle theory?

A

a model that explains how the particles in a material behave in each of the three states of matter by considering each particle as a small, solid, inelastic sphere

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36
Q

describe the structure of solids

A
  • strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement
  • particles don’t move from their positions, so all solids keep a definite shape and volume, and don’t flow like liquids
  • the particles vibrate about their positions - the hotter the solid becomes the more they vibrate
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37
Q

describe the structure of liquids

A
  • a weak force of attraction between the particles. They’re randomly arranged and free to move past each other, but they tend to stick closely together
  • liquids have a definite volume but don’t keep a definite shape, and will flow to fill the bottom of a container
  • the particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated
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38
Q

describe the structure of gases

A
  • very weak forces of attraction between particles - they’re free to move and are far apart. The particles in gases travel in straight lines.
  • don’t keep a definite shape or volume and will always fill any container
  • the particles move constantly with random motion. The hotter the gas gets, they faster they move. Gases either expand when heated, or their pressure increases
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39
Q

what are the drawbacks of particle theory?

A
  • particles aren’t solid or inelastic and they aren’t spheres - they’re atoms, ions or molecules
  • doesn’t show the forces between the particles, so there’s no way of knowing how strong they are
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40
Q

what do state symbols tell you?

A

the state of a substance in an equation

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41
Q

give the state symbols

A

(s) - solid
(l) - liquid
(g) - gas
(aq) - aqueous

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42
Q

what does aqueous mean?

A

dissolved in water

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43
Q

What is a mole?

A

One mole of any substance is an amount of that substance that contains an Avogadro number of particles (6.02 × 10^23).

One mole of any substance will have a mass in grams equal to the relative Ar or Mr of the element or compound.

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44
Q

Oxygen has an atomic mass of 16. How much would one mole of oxygen weigh?

A

16g

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45
Q

Carbon dioxide has a relative formula mass of 44. How much would one mole of carbon dioxide weigh?

A

44g

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46
Q

What is the formula to find the number of moles in a given mass?

A

Number of moles (n) = mass (m) in g / Mr

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47
Q

What mass of carbon is there in 4 moles of carbon dioxide?

Mr of carbon = 12

A

M = n × Mr
= 4 × 12
=48

There are 48g of carbon in 4 moles of carbon dioxide

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48
Q

What do the big numbers in front of the chemical formulas tell you? E.g. 2HCL

A

They tell you how many moles of each substance takes part or is formed by the reaction.
E.g. If it says 2HCl there is 2 moles of HCl in the equation.

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49
Q

what is the avogadro constant?

A

6.02 x 10^23 (the number of particles of a substance it takes for the substance to have exactly the same weight in grams as its relative atomic or formula mass)

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50
Q

if you know the masses of the reactants and products in a reaction, what are the 4 steps to working out the balanced symbol equation for the reaction using moles?

A
  1. divide the mass of each substance by its relative formula mass to find the number of moles
  2. divide the number of moles of each substance by the smallest number of moles in the reaction (i.e. the number of moles of the substance with the lowest number of moles)
  3. if any of the numbers aren’t whole numbers, multiply all the numbers by the same amount so that they all become whole numbers
  4. write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas
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51
Q

when do reactions stop?

A

when all of one of the reactants is used up - this reactant is called the limiting reactant

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52
Q

why would you add one reactant in excess?

A

to make sure that all of the other reactants are used up

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53
Q

what is the relationship between the amount of product formed in a reaction and the amount of limiting reactant? Why is this?

A

they are directly proportional, because if you add more reactant there will be more reactant particles to take part in the reaction, which means more product particles

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54
Q

what are the steps to calculating the mass of a product formed in a reaction by using the mass of the limiting reactant and the balanced symbol equation? What is another use of this method?

A
  1. work out the balanced equation
  2. work out the relative formula masses (Mr) of the reactant and product you want
  3. find out how many moles there are of the substance you know the mass of
  4. use the balanced equation to work out how many moles there’ll be of the other substance. In this case, that’s how many moles of product will be made of this many moles of reactant.
  5. Use the number of moles to calculate the mass
  6. this method could also be used to find the mass of a reactant needed to produce a known mass of product
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55
Q

what is concentration a measure of?

A

how much of a substance (e.g. the mass or the number of moles) can be found in a certain volume of a solution

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56
Q

what is the solute?

A

the substance that’s dissolved

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57
Q

give a unit of concentration

A

g/dm^3

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58
Q

give one way to measure the concentration of a solution

A

by calculating the mass of a substance in a given volume of solution. The units would be units of mass/units of volum

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59
Q

give the formula to find the concentration of a substance (include example units)

A

concentration (g/dm^3) = mass of solute (g) / volume of solvent (dm^3)

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60
Q

What are the lowest and highest pHs?

A

0 and 14

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61
Q

What colour does an acid turn the universal indicator?

What colour does an alkaline turn the universal indicator?

A 
Acid = red 
alkalis = purple
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62
Q

Is an acidic pH low or high?

Is an alkaline pH low or High?

A 
Acidic = low 
alkali = high
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63
Q

What ions do acids form in water?

A

H+

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64
Q

What ion do alkalis form in water?

A

OH-

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65
Q

What is a base?

A

A substance with a pH larger than 7

66
Q

What is pH measuring?

A

The concentration of hydrogen ions

67
Q

For every decrease of 1 on the pH scale, does the concentration of H+ ions increase or decrease, and by how much?
What about for a decrease of 2?

A

When the pH decreases by 1 the concentration of H+ ions increases by a factor of 10
when the pH decreases by 2 the concentration of H+ ions increases by a factor of 100

68
Q

What is the reactivity series?

A 
Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper
69
Q

How can you tell the reactivity of a metal by reacting it with an acid?

A

The more reactive the metal the more bubbles will be given off at a faster rate. you can also tell by how much the temperature changed, and how long the reaction lasted (the faster it goes the more reactive the acid)

70
Q

What do you get when you react an acid and a metal?

A

Salt and hydrogen

71
Q

What do you get when you react a metal and water?

A

Metal hydroxide + hydrogen

72
Q

What is the definition of an ore?

A

A metal oxide that is naturally found in rocks and contains enough metal to be economical to extract

73
Q

What is the opposite of oxidation?

A

Reduction

74
Q

Why can’t some metals be extracted using carbon?

A

They are more reactive than carbon, so carbon can’t displace them.

75
Q

Oxidation and reduction are both examples of what type of reaction?

A

A redox reaction

76
Q

What what is the name of the reaction that means ‘splitting up with electricity’?

A

Electrolysis

77
Q

If electrons are transferred, what type of reaction is it?

A

A redox reaction

78
Q

Define a strong acid.

Define a weak acid.

A

A strong acid forms H+ ions and ionises fully in aqueous solutions.
A weak acid forms H+ ions but only partially ionises in aqueous solutions.

79
Q

Define a concentrated acid.

Define a dilute acid.

A

A concentrated acid has a large mass of acid per unit volume. A dilute acid has a small mass of acid per unit volume.

80
Q

Are metal oxides and hydroxides acidic or alkaline?

A

Alkaline

81
Q

What does a reaction between an acid and a metal carbonate produce?

A

A salt, water and carbon dioxide

82
Q

What does a reaction between an acid and a metal oxide produce?
What about with a metal hydroxide?

A

They both produce a salt and water.

83
Q

What does a reaction between a metal and an acid produce?

A

A salt and hydrogen

84
Q

what is an indicator?

A

a dye that changes colour depending on whether it’s above or below a certain pH.

85
Q

what are wide range indicators?

A

indicators that contain a mixture of dyes that means they gradually change colour over a broad range of pH

86
Q

what are wide range indicators useful for?

A

estimating the pH of a solution

87
Q

which is more accurate, universal indicator or a pH probe + meter?

A

a pH probe + meter

88
Q

how can you measure pH electronically?

A
  1. attach a pH probe to a pH meter
  2. place the probe in the solution you are measuring and the pH is given on a digital display as a numerical value, meaning it’s more accurate than an indicator
89
Q

what is an acid?

A

a substance that forms aqueous solutions with a pH of less than 7. Acids form H+ ions in water

90
Q

what is an alkali?

A

a base that dissolves in water to form a solution with a pH greater than 7. Alkalis form OH- ions in water

91
Q

what is neutralisation?

A

the reaction between acids and bases

92
Q

give the formula for the reaction between an acid and a base

A

acid + base -> salt + water

93
Q

write the formula for neutralisation between acids and alkalis in terms of H+ and OH- ions

A

H+ + OH- -> H2O

94
Q

how can an indicator be used to show that a neutralisation reaction is over?

A

the products of a neutralisation reaction are neutral (i.e. they have a pH of 7), therefore an indicator can be used to show that a neutralisation reaction is over

95
Q

what do acid particles do in water?

A

they dissociate to release H+ ions

96
Q

what type of reaction is the ionisation of a weak acid? What does this allow to happen?

A

the ionisation of a weak acid is a reversible reaction, which sets up an equilibrium between the undissociated and dissociated acid.

97
Q

where does the position of equilibrium lie in the ionisation of a weak acid? why?

A

since only a few of the acid particles release H+ ions, the position of equilibrium lies well to the left.

98
Q

will strong acids be more or less reactive than weak acids of the same concentration? why?

A

more reactive - reactions of acids involve the H+ ions reacting with other substances. If the concentration of H+ ions is higher, the rate of reaction will be faster, so strong acids will be more reactive than weak acids of the same concentration

99
Q

what is the formula for the change in H+ ion concentration if you take the difference in pH to be x?

A

10^-x
(x is the difference in pH. So if pH falls from 7 to for the difference is -3, and the factor the H+ ion concentration has increased by is 10^-(-3) = 10^3 = 1000)

100
Q

name 3 strong acids

A
  1. sulfuric acid
  2. nitric acid
  3. hydrochloric acid
101
Q

why do all metal oxides and metal hydroxides react with acids to form a salt and water?

A

metal oxides and metal hydroxides are bases, and acids and bases react together to form a salt and water

102
Q

are metal carbonates acidic or alkaline?

A

alkaline

103
Q

what are the 5 steps to making soluble salts using an insoluble base?

A
  1. you need to pick the right acid and insoluble base, such as an insoluble metal oxide, hydroxide, or carbonate. E.g. if you want to make copper chloride, you could mix hydrochloric acid and copper oxide
  2. gently warm the dilute acid using a bunsen burner, then turn off the bunsen burner
  3. add the insoluble base to the acid a bit at a time, until no more reacts (i.e. the base is in excess). You’ll know when all the acid has been neutralised because, even after stirring, the excess solid will just sink to the bottom of the flask
  4. then filter out the excess solid to get to the salt solution
  5. to get pure, solid crystals of the salt, gently heat the solution using a water bath or an electric heater to evaporate some of the water (to make it more concentrated) and then stop heating it and leave the solution to cool. Crystals of the salt should form, which can be filtered out of the solution and then dried. This is called crystallisation
104
Q

what is the reactivity of metals determined by?

A

how easily they lose electrons - forming positive ions. The higher up the reactivity series a metal is, the more easily they form positive ions.

105
Q

give a method of placing metals in order of reactivity

A

when metals react with water or acid, they lose electrons and form positive ions. So, the higher a metal is in the reactivity series, the more easily it reacts with water or acid. If you compare the relative reactivity of different metals with either an acid or water and put them in order from most reactive to the least reactive, the order you get is the reactivity series

106
Q

describe a method for finding out how reactive a metal is

A

some metals react with acids to produce a salt and hydrogen gas:

  1. the speed of reaction is indicated by the rate at which the bubbles of hydrogen are given off
  2. the more reactive the metal, the faster the reaction will go. Very reactive metals like potassium, sodium, lithium and calcium react explosively, but less reactive metals such as magnesium, zinc and iron react less violently. In general, copper won’t react with cold, dilute acids
  3. you can also investigate the reactivity of metals by measuring the temperature change of the reaction with an acid or water over a set time period. If you use the same mass and surface area of metal each time, then the more reactive the metal, the greater the temperature change should be
107
Q

name 4 metals that will react with water

A

potassium, sodium, lithium and calcium will all react with water

108
Q

name 3 metals that won’t react with water

A
  1. zinc
  2. iron
  3. copper
109
Q

give the balanced symbol equation (with state symbols) for the reaction between calcium and water

A

Ca(s) + 2H2O -> Ca(OH)2(aq) + H2(g)

110
Q

give two ways to describe oxidation

A
  1. the addition of oxygen

2. a loss of electrons

111
Q

give 2 ways to describe reduction

A
  1. the removal of oxygen

2. the gaining of electrons

112
Q

are iron atoms oxidised or reduced when they react with dilute acid?

A

they are oxidised by the hydrogen ions (they lose electrons)

113
Q

when iron reacts with a dilute acid, are the hydrogen ions in the acid oxidised or reduced?

A

they are reduced by the iron atoms - they gain electrons

114
Q

what type of reactions are displacement reactions?

A

redox reactions

115
Q

choose the right words:
in a displacement reaction, the more/less reactive substance/metal/non-metal will displace the more/less reactive substance/metal/non-metal from its compound.

A

in a displacement reaction, the more reactive metal will displace a less reactive metal from its compound

116
Q

in a displacement reaction between iron and copper (iron replacing copper), which metal is oxidised and which is reduced?

A
  • the iron loses 2 electrons to become a 2+ iron - it’s oxidised
  • the copper gains these 2 electrons to become a copper atom - it’s reduced
117
Q

in displacement reactions, is it the metal ion or the metal atom that gains electrons and is reduced?

A

the metal ion

118
Q

in displacement reactions, is it the metal ion or the metal atom that loses electrons and is oxidised?

A

the metal atom

119
Q

what do ionic equations show?

A

only the particles that react and the products they form are shown - it just shows the useful bits of a reaction are shown. For example, the full equation for the displacement of zinc ions by magnesium metal is: Mg(s) + ZnCl2(aq) -> MgCl2(aq) + Zn(s), whereas the ionic equation would be Mg(s) + Zn2+ -> Mg2+ + Zn(s)

120
Q

write an ionic equation for the reaction of zinc and iron sulfate (Zn + FeSO4 -> ZnSO4 + Fe)

A

Zn + Fe[2+] -> Zn[2+] + Fe

121
Q

in the reaction between zinc and iron sulfate, which species is being reduced and which is being oxidised?

A

iron is being reduced and zinc is being oxidised

122
Q

what happens during electrolysis?

A

an electric current is passed through an electrolyte (a molten or dissolved isotonic compound). The ions move towards the electrodes, where they react, and the compound decomposes. The positive ions move towards the cathode and the negative electrons move towards the anode. This creates a flow of charge through the electrolyte as ions travel to the electrodes. As ions gain or lose electrons, they form an uncharged element and are discharged from the electrolyte

123
Q

during electrolysis, where do the positive ions in the electrolyte move? do they lose or gain electrons? are they oxidised or reduced?

A

the positive ions in the electrolyte will move towards the cathode and gain electrons (they are reduced)

124
Q

during electrolysis, where do the negative ions in the electrolyte move? do they lose or gain electrons? are they oxidised or reduced?

A

the negative ions in the electrolyte will move towards the anode and lose electrons (they are oxidised)

125
Q

what is an electrolyte? what is an electrode?

A

a liquid or solution that can conduct electricity. An electrode is a solid that conducts electricity and is submerged in the electrolyte

126
Q

why can a molten ionic compound be electrolysed, but not an ionic solid?

A

Molten ionic compounds can be electrolysed because the ions can move freely and conduct electricity. An ionic solid can’t be electrolysed because the ions are in fixed positions and can’t move.

127
Q

why should the electrodes be inert during electrolysis?

A

so they they don’t react with the electrolyte

128
Q

why is using electrolysis to extract metals very expensive?

A

lots of energy is required to melt the ore and produce the required current

129
Q

what are the steps to extracting aluminium using electrolysis?

A
  1. aluminium is extracted from the ore bauxite by electrolysis. Bauxite contains aluminium oxide, Al2O3
  2. aluminium oxide has a very high melting temperature so it’s mixed with cryolite to lower the melting point
  3. the molten mixture contains free ions - so it’ll conduct electricity
  4. the positive Al[3+] ions are attracted to the negative electrode where they each pick up three electrons and turn into neutral aluminium atoms. These then sink to the bottom of the electrolysis tank.
  5. the negative O[2-] ions are attracted to the positive electrode where they each lose two electrons. The neutral oxygen atoms will then combine to form O2 molecules
130
Q

why does the anode need to be replaced regularly when extracting aluminium from aluminium oxide?

A

the anode is made of carbon and needs to be replaced regularly as it reacts with oxygen to produce carbon dioxide

131
Q

what are the rules for the cathode during electrolysis of aqueous solutions?

A

hydrogen will always be produced unless there is a metal less reactive than hydrogen present

132
Q

what is the reactivity series?

A 
potassium
sodium
lithium
calcium
magnesium
carbon
zinc
iron
hydrogen
copper
133
Q

what are the rules at the anode during electrolysis of aqueous solutions?

A

if OH- and halide ions (Cl-, Br-, I-) are present, molecules of chlorine, bromine or iodine will be formed. If no halide ions are present, then the OH- ions are discharged and oxygen will be formed (oxygen will always be formed unless there is a halogen present)

134
Q

what do you need to remember to include when drawing the apparatus for an electrolysis experiment?

A

a d.c. power supply, wires and labels for the anode and cathode. The anode is the electrode on the same side as the longer line of the d.c. power supply symbol.

135
Q

what do half equations show?

A

the reactions at the electrodes during electrolysis

136
Q

what is the important thing to remember when you’re combining half equations?

A

the number of electrons needs to be the same for each half equation

137
Q

give the half equations for the reactions at the anode and cathode during the electrolysis of aqueous sodium chloride. What do these equations combine to form?

A

anode: 2Cl[-] -> Cl2 + 2e[-] OR 2Cl[-] - 2e[-] -> Cl2
cathode: 2H{+} + 2e{-} -> H2
these combine to form the ionic equation: 2H{+} + 2Cl{-} -> H2 + Cl2

138
Q

what is the half equation for the anode when a halide isn’t present in the aqueous solution?

A

4OH[-] -> O2 + 2H2O +4e[-] OR 4OH[-] - 4e[-] -> O2 + 2H2O

139
Q

Define an exothermic reaction

A

Energy is given out to the surroundings because more energy was given out by making bonds than was taken in for breaking bonds

140
Q

Does an exothermic reaction get warmer or colder?

A

warmer

141
Q

define an endothermic reaction

A

Energy is taken in from the surroundings because more energy was taken in for breaking bonds than was given out by breaking bonds

142
Q

does an endothermic reaction get warmer or colder?

A

colder

143
Q

Give two examples of an exothermic reaction

A

combustion, neutralization reactions

144
Q

Give two examples of endothermic reactions

A

the reaction between citric acid and sodium hydrogencarbonate, thermal decomposition (photosynthesis also counts but it isn’t in the book)

145
Q

give two uses of exothermic reactions

A

some hand warmers and self-heating cans

146
Q

give a use of endothermic reactions

A

some sports injury packs

147
Q

what are reaction profiles?

A

diagrams that show the relative energies of the reactants and products in a reaction, and how the energy changes over the course of the reaction

148
Q

If the reactants are higher than the products in a reaction profile, is the reaction exothermic or endothermic?

A

exothermic

149
Q

if the reactants are lower than the products in a reaction profile, is the reaction exothermic or endothermic?

A

endothermic

150
Q

what is the name of the initial rise of energy in a reaction profile?

A

activation energy

151
Q

what is activation energy?

A

the minimum amount of energy the reactants need to collide with each other and react. The greater the activation energy, the more energy needed to start the reaction.

152
Q

what does the overall difference in height of a reaction profile represent?

A

the overall energy change during the reaction

153
Q

Does breaking bonds require energy or release energy? Is it exothermic or endothermic?

A

It requires energy - it is endothermic

154
Q

does forming bonds require energy or release energy? is it exothermic or endothermic?

A

It releases energy - it is exothermic

155
Q

H-H: +436 kJ/mol; Cl-Cl; + 242 kJ/mol; H-Cl: +431kJ/mol

work out the total energy change for the reaction H2 + Cl2 -> 2HCl

A

-184 kJ/mol

156
Q

describe an experiment you could do to measure the amount of energy released by a chemical reaction. What is the biggest problem with this reaction? What could this method be used for?

A
  1. you can measure the amount of energy released by a chemical reaction (in a solution) by taking the temperature of the reagents, mixing them in a polystyrene cup and measuring the temperature of the solution at the end of the reaction
  2. the biggest problem with energy measurements is the amount of energy lost to the surroundings
  3. you can reduce the energy lost by putting the polystyrene cup into a beaker of cotton wool to give more insulation, and putting a lid on the cup to reduce energy lost by evaporation
  4. this method works for neutralisation reactions or reactions between metals and acids, or carbonates and acids
  5. you can also use this method to investigate what effect different variables have on the amount of energy transferred - e.g. the mass or concentration of the reactants used.
157
Q

describe an experiment to test the effect of acid concentration on the energy released in a neutralisation reaction between hydrochloric acid (HCl) and sodium hydroxide

A
  1. put 25 cm^3 of 0.25 mol/dm^3 of hydrochloric acid and sodium hydroxide in separate beakers
  2. place the beakers in a water bath set to 25 degrees C until they are both 25 degrees C
  3. add the HCl followed by the NaOH to a polystyrene cup with a lid
  4. take the temperature of the mixture every 30 seconds, and record the highest temperature
  5. repeat steps 1-4 using 0.5 mol/dm^3 and then 1 mol/dm^3 of hydrochloric acid
158
Q

what is the equation for the overall energy change of the reaction?

A

overall energy change = energy required to break bonds - energy released by forming bonds

159
Q

is a negative overall energy change endothermic or exothermic?

A

exothermic

160
Q

would an endothermic reaction have a negative or positive overall energy change?

A

positive

Chemistry (16 decks)

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