C5 Flashcards
(168 cards)
1
Q
What is meant by the rate of reaction?
A
The rate of reaction is a measure of how quickly reactants are used or products are formed:
rate of reaction = amount of reactant used / time taken
rate of reaction = amount of product formed / time taken
2
Q
How can you measure the volume of gas produced in a reaction?
A
You can measure the volume of gas using an upside-down measuring cylinder in water or a gas syringe.
3
Q
What is the reaction between magnesium and hydrochloric acid?
A
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
4
Q
What are the steps to measure how fast hydrogen is produced?
A
- Place dilute hydrochloric acid in a conical flask connected to a gas syringe.
- Add magnesium ribbon, stopper the flask, and start a stop clock.
- Record the time and volume of hydrogen at regular intervals.
- Draw a line graph of your results.
5
Q
Why is it easier to measure the volume of hydrogen produced rather than its mass?
A
Measuring the volume of gas is often easier than measuring its mass.
6
Q
How do you calculate the mean rate of reaction?
A
Mean rate of reaction = change in volume / change in time.
7
Q
What is the instantaneous rate of reaction?
A
The instantaneous rate of reaction is the rate at a particular time, calculated as the gradient of the tangent to the curve at that time.
8
Q
How much nitrogen is produced in an air bag reaction?
A
The reaction in an air bag produces 60 dm³ of nitrogen in 30 ms.
9
Q
What is the formula for calculating the mean rate of reaction in an air bag?
A
Mean rate of reaction = volume of nitrogen produced / time taken.
10
Q
What is the learning outcome of C5.1.2?
A
After studying this lesson you should be able to calculate the percentage yield of a product, define the atom economy of a reaction, and calculate the atom economy of a reaction.
11
Q
What is sustainable development?
A
Sustainable development is the idea that you should meet your needs without damaging the ability of future generations to meet their needs.
12
Q
How do you calculate percentage yield?
A
Percentage yield = (actual yield / theoretical yield) * 100
13
Q
What is the percentage yield if the theoretical yield is 8.00 g and the actual yield is 7.10 g?
A
Percentage yield = (7.10 g / 8.00 g) * 100 = 88.8% to three significant figures.
14
Q
What affects percentage yield?
A
Percentage yield may be less than 100% due to unexpected reactions, incomplete reactions, or product loss during separation.
15
Q
How do you calculate atom economy?
A
Atom economy = (sum of M of the desired product / sum of M of all products) * 100
16
Q
What is the atom economy for producing hydrogen from methane and steam?
A
Atom economy = (6.0 / 34.0) * 100 = 17.6% to three significant figures.
17
Q
What is a study tip regarding percentage yield and atom economy?
A
Percentage yield and atom economy cannot be greater than 100%.
18
Q
What is the learning outcome of C5.1.3 Choosing a reaction pathway?
A
After studying this lesson you should be able to explain why a particular reaction pathway is chosen to produce a specified product, using appropriate data.
19
Q
What is ethanediol used for in car screenwash?
A
Ethanediol is an antifreeze made from epoxyethane, used to stop car screenwash from freezing in winter.
20
Q
What factors do chemical engineers consider when choosing a reaction pathway?
A
Chemical engineers consider yield of the product, atom economy of the reaction, usefulness of by-products, rate of the reaction, and equilibrium position if reversible.
21
Q
Why do manufacturers need to make a profit when producing substances?
A
Manufacturers must make a profit to avoid going out of business.
22
Q
What was the original method for making epoxyethane?
A
The original method involved two steps: ethene + chlorine + water → chloroethanol + hydrogen chloride, and chloroethanol + calcium hydroxide → calcium chloride + water + epoxyethane.
23
Q
What was the yield and atom economy of the original epoxyethane process?
A
The yield was about 80%, and the atom economy was 25.4%.
24
Q
What is the modern process for making epoxyethane?
A
The modern process uses one step: ethene + oxygen → epoxyethane, with a yield of about 80% and an atom economy of 100%.
25
What is a by-product?
A by-product is a substance formed in a reaction in addition to the desired product.
26
How can by-products affect atom economy?
If a by-product is useful and can be sold, it improves the atom economy of a process.
27
What is one use of calcium chloride, a by-product of the original epoxyethane process?
Calcium chloride is used as an additive in concrete and polymers and to trap moisture in de-humidifiers.
28
What is the atom economy of the original epoxyethane process after selling calcium chloride?
The atom economy improved to 89.6%.
29
What are three factors that affect the choice of reaction pathway for making a substance?
Yield of the product, atom economy, and usefulness of by-products.
30
What are the two methods of manufacturing ethanol?
Ethanol can be manufactured by reacting ethene with steam or by fermentation of plant sugars.
31
What is the atom economy and yield of the fermentation process for ethanol?
The atom economy is 51.1% and the yield is 95%.
32
What does the term 'by-product' mean?
A by-product is a substance formed in a reaction in addition to the desired product.
33
How can selling carbon dioxide as a by-product affect the choice of process for making ethanol?
Selling carbon dioxide to fizzy drinks manufacturers may make the fermentation process more desirable due to additional revenue.
34
What should you be able to calculate after studying C5.1.4?
You should be able to calculate concentration of solution in mol/dm³ and explain the relationship between concentration of solution, mass of solute, and volume of solution.
35
What is the relationship between cubic centimetres and cubic decimetres?
One litre is one cubic decimetre, so one millilitre is one cubic centimetre.
36
How do you convert from cm³ to dm³?
Divide by 1000 to convert from cm³ to dm³.
37
How do you convert from dm³ to cm³?
Multiply by 1000 to convert from dm³ to cm³.
38
How do you calculate concentration in g/dm³?
Concentration in g/dm³ = mass of solute in g / volume of solution in dm³.
39
What is the concentration of a solution containing 4.5 g of solute in 250 cm³?
The concentration is 18 g/dm³.
40
How do you calculate concentration in mol/dm³?
Concentration in mol/dm³ = amount of solute in mol / volume of solution in dm³.
41
What is the concentration of a solution containing 5.85 g of sodium chloride in 125 cm³?
The concentration is 0.8 mol/dm³.
42
How do you convert between concentration units?
To convert mol/dm³ to g/dm³, multiply by the molar mass of the solute. To convert g/dm³ to mol/dm³, divide by the molar mass.
43
What is the molar mass of sodium chloride (NaCl)?
The molar mass of NaCl is 58.5 g/mol.
44
How do you calculate the amount of solute in mol?
Amount of solute in mol = mass in g / molar mass in g/mol.
45
How do you calculate the volume of solution in dm³?
Volume of solution in dm³ = amount of solute in mol / concentration in mol/dm³.
46
What is the concentration of a solution containing 0.450 g of sodium chloride in 50.0 cm³?
Give your answer to three significant figures.
47
How do you calculate the mass of potassium iodide (KI) for a 0.125 mol/dm³ solution?
Calculate the mass required to make 0.500 dm³ of a 0.125 mol/dm³ solution.
48
What is a titration?
A titration is a technique that uses a neutralisation reaction to find the concentration of an acid or an alkali.
49
What apparatus is used in titrations that has a tap and graduated scale?
A burette.
50
How do you prepare a standard solution for titration?
Dissolve 1.00 g of NaOH in about 150 cm³ of water, then transfer to a 250 cm³ volumetric flask and add water to reach the 250 cm³ mark.
## Footnote
This standard solution has a concentration of 0.100 mol/dm³.
51
What precautions should be taken before carrying out a titration?
Use a volumetric pipette for accuracy, clamp the burette vertically, and wear eye protection.
52
Why is a volumetric pipette preferable to a measuring cylinder in titrations?
A volumetric pipette is more accurate than a measuring cylinder.
53
What is the titre in a titration?
The titre is the volume of acid added to the alkali in the flask, calculated from the initial and final burette readings.
54
What techniques ensure a repeatable titre in titrations?
Swirl the flask, perform a rough first titration, and add acid drop by drop in subsequent runs.
55
What is meant by concordant titres?
Concordant titres are titres that are within 0.10 cm³ of each other.
56
What should be recorded for burette readings in a titration?
Record readings to two decimal places, ending in 0 if on a line or 5 if between lines.
57
What is the purpose of carrying out a titration?
To determine the concentration of an acid or alkali.
58
What should you be able to do after studying C5.1.7 Gas calculations?
Describe the relationship between molar amounts of gases and their volumes, and calculate the volumes of gases involved in reactions using the molar gas volume.
59
What is the molar volume at room temperature and pressure (RTP)?
One mole of any substance in the gas state occupies 24 dm³/mol (24,000 cm³/mol) at RTP.
60
What is the equation linking the amount and volume of a gas at RTP?
Volume in dm³ = Amount in mol x 24 dm³/mol.
61
How do you calculate the amount of gas if you know its volume?
Amount in mol = Volume in dm³ / 24 dm³/mol.
62
How can you use the molar volume?
You can calculate the volume of a gaseous reactant or product if you know its amount, or the amount of a gaseous reactant or product if you know its volume.
63
What happens to molar volume if pressure decreases or temperature increases?
Molar volume increases.
64
What is the ideal gas law equation?
pV = nRT.
65
How do you calculate the volume of hydrogen produced from 1.31 g of zinc reacting with sulfuric acid?
1. Calculate the amount of zinc: 0.0200 mol. 2. Use the balanced equation to find hydrogen produced: 0.0200 mol. 3. Calculate volume: 0.48 dm³.
66
What is the method to measure the volume of gas produced in a reaction?
Fill a measuring cylinder with water, turn it upside down underwater, clamp it, mix reactants in a conical flask, and measure the volume of gas produced.
67
What should be worn during the practical investigation of measuring gas volume?
Eye protection.
68
What is the mass of 1 cm³ of water?
1 cm³ of water has a mass of 1 g.
69
What is meant by the rate of reaction?
The rate of reaction is a measure of how quickly reactants are used or products are formed:
rate of reaction = amount of reactant used / time taken
rate of reaction = amount of product formed / time taken
70
How can you measure the volume of gas produced in a reaction?
You can measure the volume of gas using an upside-down measuring cylinder in water or a gas syringe.
71
What is the reaction between magnesium and hydrochloric acid?
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
72
What are the steps to measure how fast hydrogen is produced?
1. Place dilute hydrochloric acid in a conical flask connected to a gas syringe.
2. Add magnesium ribbon, stopper the flask, and start a stop clock.
3. Record the time and volume of hydrogen at regular intervals.
4. Draw a line graph of your results.
73
Why is it easier to measure the volume of hydrogen produced rather than its mass?
Measuring the volume of gas is often easier than measuring its mass.
74
How do you calculate the mean rate of reaction?
Mean rate of reaction = change in volume / change in time.
75
What is the instantaneous rate of reaction?
The instantaneous rate of reaction is the rate at a particular time, calculated as the gradient of the tangent to the curve at that time.
76
How much nitrogen is produced in an air bag reaction?
The reaction in an air bag produces 60 dm³ of nitrogen in 30 ms.
77
What is the formula for calculating the mean rate of reaction in an air bag?
Mean rate of reaction = volume of nitrogen produced / time taken.
78
What should you mention when explaining changes in rates of reaction?
Mention the rate or frequency of collisions rather than just the 'number' of collisions.
79
What is the learning outcome for C5.2.2?
Describe and explain the effect of changes in temperature on the rate of reaction.
80
How do chemical reactions behave at higher temperatures?
Chemical reactions go faster at higher temperatures.
81
What two conditions must be met for a reaction to happen?
Reactant particles must collide with each other and have enough energy to react.
82
What is a successful collision?
A collision that leads to a reaction.
83
What happens to particle movement as temperature increases?
Particles move more quickly, leading to more frequent collisions.
84
What is the relationship between successful collisions and reaction rate?
The greater the rate of successful collisions, the greater the rate of reaction.
85
What reaction is often used to investigate factors affecting rates of reaction?
The reaction between sodium thiosulfate solution and hydrochloric acid.
86
What safety precautions should be taken during the sodium thiosulfate experiment?
Place beakers in an ice bath to reduce fumes and ensure the room is well ventilated.
87
How can you measure the rate of reaction in the sodium thiosulfate experiment?
By timing how long it takes for a pale yellow precipitate of sulfur to appear.
88
What does a longer time for the cross to disappear indicate?
A lower rate of reaction.
89
What is the relationship between rate of reaction and reaction time?
The rate of reaction is inversely proportional to the reaction time.
90
How can you calculate the rate of reaction from reaction time?
Rate of reaction = 1/reaction time.
91
What is the rate of reaction for a reaction time of 10 seconds?
0.10/s.
92
What alternative calculation can be used for rate of reaction?
1000/reaction time.
93
What happens to the rate of reaction if the temperature is decreased?
The rate of reaction decreases.
94
What does Figure 3 illustrate?
Reaction time decreases as the temperature increases.
95
What does Figure 4 illustrate?
The rate of reaction increases as the temperature increases.
96
Estimate the rate of reaction at 45 °C from Figure 4.
Refer to Figure 4 for the estimate.
97
Why does the rate of reaction double between 60 °C and 80 °C?
Explain in terms of particles and energy.
98
Why are there no results below 20°C or above 80°C?
Suggest reasons based on experimental conditions.
99
What is the effect of changes in concentration of solutions on the rate of reaction?
The rate of reaction increases as the concentration increases because the particles become more crowded, leading to more frequent collisions.
100
What is the concentration of a solution?
The concentration of a solution is a measure of how much solute is dissolved in the solvent.
101
Why do reactions go faster at higher concentrations?
Reactions go faster at higher concentrations because the particles collide more often due to being more crowded.
102
What happens to the reaction rate when hydrochloric acid is mixed with water?
The reaction rate decreases when hydrochloric acid is mixed with water because the concentration of the acid is reduced.
103
How can you investigate the effect of concentration on reaction rate?
You can investigate this by measuring the time taken for a piece of magnesium ribbon to be used up in the reaction with hydrochloric acid at different concentrations.
104
What must be controlled during the investigation of concentration on reaction rate?
The length of the magnesium ribbon must be controlled to ensure a fair test.
105
Why should the temperature be kept the same when investigating the effect of concentration on reaction rate?
Keeping the temperature the same ensures that it does not affect the reaction time.
106
What is a limiting reactant?
In a reaction involving two reactants, the limiting reactant is the one that is completely consumed first, determining the amount of product formed.
107
Why do reactions go faster at higher pressures?
Reactions go faster at higher pressures because the gas particles become more crowded, leading to more frequent collisions.
108
What happens to the rate of reaction if the pressure is increased?
The rate of reaction increases as the pressure of the gas increases due to more frequent collisions.
109
What is the relationship between the volume of gas produced and the amount of magnesium used?
The volume of gas produced is proportional to the amount of the limiting reactant used.
110
What is the learning outcome of C5.2.4?
After studying this lesson you should be able to describe, and explain, the effect on the rate of reaction of changes in the size of pieces of a reacting solid.
111
Why do reactions go faster with powders?
The rate of reaction increases as the surface area increases because more reactant particles are available for collisions and collisions are more likely.
112
What happens to the surface area to volume ratio as the size of lumps decreases?
As the size of the lumps decreases, the surface area to volume ratio increases.
113
What is the reaction between calcium carbonate and hydrochloric acid?
CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)
114
How can the volume of carbon dioxide gas produced be measured?
You could use a gas syringe or weigh the reaction mixture.
115
Why should the same mass of calcium carbonate be used in investigations?
To ensure that the results are consistent and comparable.
116
What effect does not using cotton wool have during the reaction?
The measured rate would be affected as hydrochloric acid could escape as a fine spray.
117
Why should temperature and concentration be kept the same in investigations?
To ensure that these variables do not affect the rate of reaction.
118
What factors influence the choice of method to measure the rate of a reaction?
The properties of the reactants and products, and the ease of measuring their loss or production.
119
Why would custard powder be a hazard in a factory?
Custard powder can create dust that may ignite and cause explosions.
120
What is a catalyst?
A catalyst is a substance that increases the rate of a reaction but is unchanged at the end of the reaction.
121
What happens to the amount of catalyst after a reaction?
If you add 1 g of catalyst to a reaction mixture, there will still be 1 g left when the reaction has finished.
122
Are catalysts specific to reactions?
Yes, catalysts are specific to particular reactions.
123
What is the role of catalysts in catalytic converters?
Catalytic converters speed up reactions that convert harmful substances in exhaust gases into less harmful ones.
124
What metals are commonly used in catalytic converters?
Platinum, rhodium, and palladium are commonly used in catalytic converters.
125
What is the purpose of using a fine mesh of platinum and rhodium in the manufacture of nitric acid?
The fine mesh increases the surface area for the reaction and helps catalyse the reaction between ammonia and oxygen.
126
What is an enzyme?
Enzymes are proteins that act as catalysts in biological systems.
127
What is catalytic activity?
Catalytic activity refers to the ability of a substance to catalyse or speed up a reaction.
128
How do catalysts work?
Catalysts provide an alternative reaction pathway with a lower activation energy.
129
What happens to the rate of successful collisions in the presence of a catalyst?
The rate of successful collisions increases compared to the rate in an uncatalysed reaction.
130
What is the effect of temperature on enzyme-catalysed reactions?
As temperature increases, the rate of a reaction catalysed by an enzyme also increases.
131
How does powdered manganese(IV) oxide (MnO2) function in a reaction?
MnO2 catalyses the decomposition of hydrogen peroxide.
132
What must be kept constant when investigating a catalyst?
The volume, temperature, and concentration of hydrogen peroxide must be kept the same.
133
What are reversible reactions?
In a reversible reaction, the products can react together to form the original reactants.
134
Give an example of a reversible reaction.
The reaction between copper(II) sulfate and water is a reversible reaction.
135
What is the formula for hydrated copper(II) sulfate?
The formula for hydrated copper(II) sulfate is CuSO₄·5H₂O.
136
What happens when you heat hydrated copper(II) sulfate?
When heated, blue hydrated copper(II) sulfate decomposes to form white anhydrous copper(II) sulfate and water.
137
What does the = symbol represent in reversible reactions?
The = symbol combines the forward reaction and backward reaction.
138
What is dynamic equilibrium?
Dynamic equilibrium occurs when the rates of the forward and backward reactions become equal in a closed system.
139
What happens to concentrations at equilibrium?
At equilibrium, the concentrations of all the reacting substances remain constant.
140
What is the significance of a closed system in reversible reactions?
In a closed system, no substances can enter or leave, allowing dynamic equilibrium to be established.
141
What is water of crystallisation?
Water of crystallisation refers to the water molecules in the ionic lattice of hydrated compounds.
142
What is the full name for hydrated cobalt(II) chloride?
The full name for hydrated cobalt(II) chloride is cobalt(II) chloride hexahydrate.
143
What is an example of a reaction that produces ammonium chloride?
Ammonium chloride decomposes when heated: NH₄Cl(s) = NH₃(g) + HCl(g).
144
How do concentrations of bromine change at equilibrium?
At equilibrium, the concentrations of bromine in the liquid state and gas state remain constant.
145
What is the balanced equation for nitrogen reacting with hydrogen to form ammonia?
The balanced equation is N₂(g) + 3H₂(g) = 2NH₃(g).
146
What is the equilibrium position?
The equilibrium position gives you an idea of the ratio of the equilibrium concentrations of products to reactants.
## Footnote
The equilibrium position is on the left when the concentration of reactants is greater than the concentration of products, and on the right when the concentration of reactants is less.
147
What happens to the equilibrium position if pressure is increased?
The equilibrium position moves in the direction of the fewest moles of gas.
## Footnote
For example, in the reaction 2SO2(g) + O2(g) → 2SO3(g), if pressure is increased, the equilibrium position moves to the right.
148
How do you determine the effect of increasing pressure on equilibrium?
Step 1: Count the total number of moles of gas on each side of the balanced equation. Step 2: Determine which side has the fewest moles of gas.
149
What happens to the equilibrium position if concentration is increased?
The equilibrium position moves in the direction away from that substance.
## Footnote
For example, in the reaction 2K2Cr2O7(aq) + H2SO4(aq) = K2Cr2O7(aq) + H2O(l) + K2SO4(aq), if the concentration of sulfuric acid is increased, the equilibrium position moves to the right.
150
What happens to the equilibrium position if temperature is increased?
The equilibrium position moves in the direction of the endothermic change.
## Footnote
For example, in the reaction 2NO2(g) = N2O4(g) (ΔH = -58 kJ/mol), if temperature is increased, the equilibrium position moves to the left.
151
What does a negative ΔH indicate about a reaction?
A negative ΔH indicates that the forward reaction is exothermic and the backward reaction is endothermic.
152
What is the effect of reducing pressure inside a sealed container at equilibrium?
Reducing the pressure will shift the equilibrium position towards the side with more moles of gas.
153
What does it indicate if very little CaO and CO2 are present at room temperature?
It indicates that the equilibrium position favors the reactants at room temperature.
154
What is the effect of adding ammonium chloride to the reaction Fe3+(aq) + SCN-(aq) = FeSCN2+(aq)?
Adding ammonium chloride reduces the concentration of Fe3+(aq), shifting the equilibrium position to the left.
155
What should you be able to explain after studying C5.3.3?
Appropriate conditions to produce a particular product using a reversible reaction.
156
What is the effect of increasing pressure on the equilibrium yield of methanol?
The equilibrium position moves to the right, increasing the equilibrium yield of methanol.
157
Why do chemical engineers not choose very high pressures for methanol production?
High pressures require expensive equipment, a lot of energy, and tough reaction vessels.
158
What is the compromise pressure for methanol production?
5-10 MPa (between 50 and 100 times normal atmospheric pressure).
159
What is the effect of increasing temperature on the equilibrium yield of methanol?
The equilibrium position moves to the left, decreasing the equilibrium yield of methanol.
160
Why do chemical engineers choose a compromise temperature for methanol production?
It needs to be low enough for a reasonable equilibrium yield but high enough for a reasonable rate of reaction.
161
What is the reaction for making methanol?
CO(g) + 2H₂(g) = CH₃OH(g)
## Footnote
(ΔH = -91 kJ/mol)
162
What factors affect the equilibrium yield?
Pressure, temperature, and concentration of reactants.
163
What does Le Chatelier's principle state?
'When a change is made to a reaction at equilibrium, the position of equilibrium moves to oppose the change.'
164
What happens when methanol is removed from the equilibrium mixture?
The equilibrium position moves to the right.
165
What is the reaction for manufacturing ethanol?
C₂H₄(g) + H₂O(g) = C₂H₅OH(g)
## Footnote
(ΔH = -45 kJ/mol)
166
What is the effect of increasing pressure on the position of equilibrium?
It shifts to the side with fewer moles of gas.
167
What is the effect of increasing temperature on the position of equilibrium?
It shifts to the endothermic direction.
168
Why are catalysts used in reversible reactions?
They do not change the equilibrium position but increase the rate of reaction.
