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Flashcards in Energetics Deck (149):
1

What is energetics?

the energy changes that take place with the surroundings during a chemical reaction

2

What is an exothermic reaction?

reactions that produce heat

3

Give examples of an exothermic reaction?

combustion (burning)

respiration

neutralisation (acid and alkali)

4

What is an endothermic reaction?

reactions that absorb/require heat to occur

5

Give examples of an endothermic reaction?

evaporation (heat the water)

ice cube melting

thermal decomposition

6

Why is an ice cube melting endothermic?

 H20 from a solid to a liquid happens from tempratures of 0to 220

water is melting, absorbing heat

7

How are exothermic and endothermic reactions represented?

they are represented graphically

energy profile diagrams

8

What is △H (between products)?

the difference in energy between the products and reactions in a chemical is known as the energy change △H

H products - H reactants

9

What does kJ stand for?

kilojoules

10

What does △ stand for?

change

11

What does H stand for?

enthalpy

12

Endothermic reactions have a (positive/negative)△H?

positive

 

13

Exothermic reactions have a (positive/negative) △H?

negative

14

Why do exothermic reactions have a negative △H?

Their products have less energy than their reactants

15

Why do endothermic reactions have a positive △H?

their products have more energy than thier reactants

16

What is activation energy (EA)?

the minimum amount of energy required between two or more reactants to overcome their mutual repulsion (e.g. two magnets repelling)

17

What is bond enthalpy (energy)?

the average energy required to break one mole of stated bond

18

Energy is required to (make/break bonds - it is an (exothermic/endothermic) process?

Energy is required to break bonds - it is an endothermic process

19

Energy is (given/taken) when bonds are made - it is an (endothermic/exothermic) process

energy is given when bonds are made- it is an exothermic process

20

Endothermic Profile Diagram

21

Exothermic Profile Diagram

22

Is bond making exothermic or endothermic? 

exothermic

23

Is bond breaking endothermic or exothermic?

endothemic

24

What are the three types of △H?

△H = H products - H reactants (theoretical)

△H = sum bonds broken - bonds made (theoretical)

△H = mc△T/n (experimental)

25

What is enthalpy?

energy change for a reaction

26

Is a negative energy change exothermic or endothermic? Why?

exothermic

the energy given out when new bonds are made is greater than the energy taken to break the original bonds

27

Is a positive energy change exothermic or endothermic? Why?

endothermic

the energy taken in to break the original bonds is greater than the energy given out when new bonds are made

 

28

Exothermic reaction △H is negative/positive?

negative

29

Endothermic reaction △H is negative/positive?

positive

30

In terms of products and reactants why would an endothermic reaction be positive?

their products have more energy than their reactants

31

In terms of products and reactants, why are exothermic reactions negative?

their products have less energy than their reactants

32

How do you measure enthalpy changes for reactions experimentaly?

by burning a substance, measuring the temprature change it causes, then calclutaing the enthalpy from the formula

33

What is the equation for speed?

speed = distance/time

34

What does -1 mean?

per something 

e.g. 30 m/s or 30 ms-1

35

What is the equation for a-1

1/a

36

What do all combustion experiments have in common?

they are all exothermic and therefore have a negative Q ( heat released)

37

How do you carry out an energy of different types of alcohol combustion experiment?

a known mass of fuel is burned in a spirit burner and the temprature rise of the known mass of water is measured

from this you calculate the energy given out by the fuel in kJ per gram

from your results you will compare the relative values obtained 

38

In the different types of alcohol combustion experiment which is 

a) the independant variable

b) the dependant variable

c) the continuos variable

a) the type of alcohol

b) temprature of water

c) mass difference of burner

39

If the temprature of 4.18 kJ per Kg per K, what does this mean?

it takes 4.18 Joules of energy to raise one Kg of water by one Kelvin. one Kelvin is equivalent to 0C

40

How is the mass of fuel burned calculated?

measure the mass of the burner before and after the experiment and then calculate the difference

41

In the differnet types of alcohol combustion experiment what could be sources of error?

scale error

human error

heat is lost to the surroundings (out of our control)

can't burn all alcohol

42

Why do differnet fuels have different energies of combustion?

some react better with oxygen

43

What does equilibrium mean?

balance

in a chemical equilibrium, the concentration of reactants and products do not change

 

44

What is static equilibrium?

once equilibrium is reached there is not more movement

45

What is dynamic equilibrium?

when the rate (speed) of the fowards reaction is equal to the rate of the reverse, so the net change is 0

 

46

What two things does a dynamic equilibrium need?

a closed system (closed experiment, no 'matter' can be exhanged with the surroundings, occurs in a sealed container)

reversible

47

Is a phase change a reaction?

No but it can still have a dymanic equilibrium

48

What is the position of equilibrium (P.O.E)?

whether the reaction is moving left to right or right to left

49

What three main factors affect the position of equilibrium/dynamic equilibrium?

temprature

concentration of reactants (amounts)

pressure (gases)

50

What is a system?

a chemical reaction

51

What is Le Chatelier Principle?

when a change is exerted on a system in a dynamic equilibrium the position of equilibrium moves to the exact opposite

52

What would happen if you increased the pressure of reactants?

the position of equilibrium would move to the right (more S03)

this is because there are two molecules on the right but three on the left therefore the right has less pressure

53

What would happen if you increased the temprature?

the position of equilibrium would move to the left

this is because the left is the endothermic direction which absorbs heat therefore the amount of product S03 would decrease

 

54

What would happen if you increased the concentration of S0and 02?

the position of equilibrium would move right

this is because it wants to remove excess reactants which moves to form products

55

What can reversible reactions do?

go fowards or backwards

56

In a closed system, a reversible reaction can reach a point of equilibrium. The amount of reactants and products (stays the same/can change). This is becaus the fowards and backward reaction is happening at the (different/same) time (....... equilibrium)

stays the same

same time

dynamic

57

What do strong acids do when dissolved in water?

split almost completely into ions when dissolved in water

58

With weak acids the ions are in what with the undissociated molecules in the acids?

equilibrium

59

Acids are proton (H+) what?

donors

60

Bases are proton (H+) what?

acceptors

61

What is a reactant?

a substance present at the start of a chemical reaction

62

What is a product?

a substance formed in a chemical reaction

63

When reversible reactions reach equilibrium the foward and reverse actions are (still happening/stopping) but at the (same/different) rate so the concentrations of reactants and products (change/do not change)

still happening

same 

do not change

64

What is a catalyst?

changes the rate of chemical reaction without being changed by the reaction itself 

65

If we remove the products from an equilibrium mixture, what happens?

more reactants are converted into products

66

If a catalyst is used what happns to the equilibrium?

it is reached must faster because the catalyst speeds up the reactants and products by the same amount

67

Does a catalyst affect the concentration of reactants and products?

no

68

 What happens if the foward reaction is exothermic and the temprature is increased?

the yield of products is decreased

69

What happens id the foward reaction is exothermic and the temprature is deacreased?

the yield of products is increased

70

What will happen if the foward reaction is endothermic and the temprature is increased?

the yield of product will increased

71

What will happen if the foward reaction is endothermic and the temprature is decreased?

the yield of prduct is decreased

72

What is the equation for Calorimetry?

73

reversible reaction; goes fowards and backwards at the same time

74

-20

75

CHECK

-103

76

-95

77

CHECK ALL OF THESE

-124

78

-590

79

An example of an equilibrium problem

80

In an experiment, 1.56g of propan-1-ol (CH3CH2CH2OH) was completely burned in air. The heat evolve raised the temprature of 0.250 litres of water from 292.1K to 339.4K. Use this data to calculate the energy of combustion per gram of propan-1-ol (the specific heat capacity of water is 4.18 Jg-1 K-1)

81

In an experiment 1.00g of propanone (CH3COCH3) was completely burned in air. The heat evolved raised the temprature of 150g of water from 18.8 to 64.3 0C. Use this data to calculate the energy of combustion per gram of propanone (the specific heat of water is 4.18 Jg-1K-1​)

82

50cm3 of 1.0 mol dm-3 hydrochloric acid was added to 50 cm3 of 1.0 mol dm-3 sodium hydrochloric solution. The temprature rose by 6.80C. Calculate the energy of neutralisation for this reaction. Assume that the specific heat capacity of the sloution is 4.18 Jg-1K-1​

83

What is reversible reaction?

a chemical reaction which can go both ways 

the direction of the reaction depends on the condition of the reactants

84

What is a catalyst?

a catalyst changes the rate of a chemical reaction without being changed by the reaction itself

85

In the Haber process what are the three raw materials used in the process?

natural gas

air

water

86

In the Haber process name a by-product of the process

carbon dioxide

87

In the Haber process what could be used to remove this by-product from the mixture of gases?

potassium carbonate (alkali)

88

In the Haber process what is the name of the catalyst used?

iron

89

The graph shows the yield of ammonia produced at equilibrium under different conditions of temprature and pressure. If the conditions are 200 atmospheres and 4250C, what yield of ammonia is obtained at equilibrium?

CHECK

33

90

The graph shows the yield of ammonia produced at equilibrium under different conditions of temprature and pressure. In practice, under the conitions of 200 atmospheres and 425oC, the yield obtained in the plant under these conditions is 15%. Suggest why this is so.

the system has not yet reached equilibrium

91

What would be the effect on the yield of ammonia of increasing the pressure? (ammonia is produced at equilibrium under conditions of temprature and pressure)

increasing the pressure increases the yield of ammonia

92

Suggest why the Haber process is not operated at even highe pressures.

increasing the pressure of gases is expensive

operating at a higher pressure means pipework is more expensive to resist explosion

93

What would be the effect of the yield of ammonia made by the Haber process by decreasing the temprature?

lowering the temprature increases the yield

94

Suggest why the Haber process is not operated at even lower temprature

lowering the temprature slows down the rate of reactions

95

Use the graph data to explain how ammonia can be removed frim the mixture of gases at atmospheric pressure

cool gases below -330C, ammonia liquifies and can be removed

96

The boiling point of these gases atre higher at higher pressure. Use your knowledge of particles to explain this

at higher pressure particles are closer together

stronger forces between particles have to be broken down

97

Some of the ammonia is distributed as liquid ammonia by road using tankers. Suggest an advantage of distributing ammoniaa as a liquid rather than as a gas. Use your knowledge of particles in your asnwer

In a liquid the oarticles are much closer together

More ammonia can be contained in a given volume

98

The air contains noble gases such as argon. What happens to these noble gases during the process?

Noble gases are not reacted and, as unreacted gases are re-cycled, their concentrations will build up

99

Describe the conditions used in the Haber process to increase the rate of reaction

100

Describe and explain the conditions used in the manufacture of ammonia to increase the yield

101

What is the Haber process used to do?

to make NH3 (l)

ammonia (alkali)

102

What can ammonia be used for?

fertilisers

103

Why do you need a compromise temprature in the Haber process?

the foward reaction is exothermic - the yield of product at equilibrium is increased at lower tempratures

if the temprature is too low the rate of reaction will be too low making the process uneconomical

a compromise is chosen - low enough to get a good yield of ammonia but high enough to obtain a reasonable rate of reaction

104

What catalyst is used in the Haber process reaction and what affect does it have?

iron filings - Fe

it does not affect the position of equilibrium but does affect the rate of reaction

ammonia is produced in a shorter time, reducing the cost of the process

iron is a cheap catalyst

105

How is the ammonia taken from the Haber process and why?

in its cool state it is tapped off as it is formed otherwise the equilibrium would move to the left

 

106

How much ammonia is produced from the Haber process?

yield = 18%

107

What is the pressure of the Haber process?

200-250 atmospheres

(we're under 1 atmosphere)

108

What is the tenprture of a Haber process?

4500C

109

What is the Haber process reaction?

110

What is a molecule?

a molecule is a collection of two or more atoms held together by chemical bonds - the fundamental unit of compounds

111

How many molecules are on each side of the Haber process?

left - 1+3 = 4 molecules of gas

right - 2 molecules of gas

112

What will happen if the pressure is increased in the Haber process?

an increase in pressure will make the position of equilibrium move to the reaction which produces the smallest number of molecules

in the Haber process this is the forward reaction

more ammonia is produced

113

Why is the pressure only so high?

there is a limit to the pressure which can be used industrially 

high pressures require very storng and expensive quiptment

 

114

Explain the choice of high pressure for the Haber process?

a compromise is chosen

high enough to get a good yielf of ammonia

low enough that it wouldn't add to much to the costs of the process

115

is burning petrol in a car exothermic or endothermic?

exothermic

116

is respiration in living cells exothermic or endothermic?

exothermic

117

is heating water to make it boil exothermic or endothermic?

endothermic

118

is thermal decomposition of limestone into limes and CO2 exothermic or endothermic?

endothermic

119

is the reaction of magnesium with oxygen exothermic or endothermic?

exothermic

120

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

how can you tell that the reaction to produce blue crystals is endothermic?

moving to oppose change pink to blue

121

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

how could you change the blue crystals to pink cyrstals?

cool down (heat goes foward) 

use an ice bath

122

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

what temperature would you observe when this is done?

increase because its exothermic

123

when heated continuously, pink cobalt chloride cyrstals can be changed into blue crystals

CoCl2 • 6H2O (pink) ⇌ CoCL2 • 2H2O + 4H2O (blue)

the symbol ⇌ tells you that the reaction is reversible

the pink cobalt chloride cyrstals have water trapped inside their crystal structure

blue cobalt chloride crystals have less water trapped insdie their crystals

suggest how the colour changes of these crystals could be used

thermometers in a room

124

many fuels ontain sulphur as an impurity

state the gas that forms when sulphur burns in air and describe the environmental effect of this gas in the atmosphere

sulphur dioxide is formed

when mixed with air particles an help form acid raid which in turn damages buildings, wildlife and water resources

125

chose the best conditions for the Haber process and explain why they would produce a high yield of ammonia and why they are used in industry

2000atm and 4500oC

200atm and 450oC

20atm and 450C

200atm and 450oC

450oC is a compromise of temperature

it is best in this reaction to use an extremely low temperature to increase the yield of product but this is uneconomical as the rate of reaction is too low so you must have a compromise of 450oC

200atm is a relatively high pressure to increase the yield of ammonia  but if it is any higher it is too expensive and there is a danger of explosions

ONE MORE MARK CHECK

 

126

brown nitrogen dioxide, NO2, exists in equilibrium with colourless dinitrogen tetroxide, N2O4

2NO2 (g) ⇌ N2O(g) 

ΔH = -57.2 kJ mol-1

the pressure is increased. when equilibrium is restored, the appearance of the mixture of gases will be:

a) colourless

b) unchanged 

c) paler brown

d) darker brown

c) paler brown

the reaction moved foward with the increase in pressure

127

brown nitrogen dioxide, NO2, exists in equilibrium with colourless dinitrogen tetroxide, N2O4

2NO2 (g) ⇌ N2O4 (g) 

ΔH = -57.2 kJ mol-1

the temperature is increased. when equilibrium is restored, the appearance of the mixture of gases will be:

a) colourless

b) unchanged 

c) paler brown

d) darker brown

d) darker brown

the reaction moved backwards 

CHECK BACKWARDS SHIZ

128

in the catalytic converter of a car engine's exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

state the effect, if any, on the position of equilibrium if the temperature is lowered

give a reason for your answer

effect = increase in exothermic direction

reason = endothermic reactions absorb heat so if the temperature is lowered then temperature needs to be released (exothermic) to restore equilibrium

129

in the catalytic converter of a car engine's exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

the gases from the engine are not cooled before entering the converter

explain why this is so

higher temperature increases the rate of reaction and so it is economical for the system to have a lower temperature 

higher temperature = particles on left have activation energy

130

in the catalytic converter of a car engine's exhauset system, the following reaction occurs:

2NO(g) + 2CO(g) ⇌ N2(g) + 2CO2(g)

ΔH = -745 kJ mol-1

the temperture in a catalytic converter is high

state the effect, if any, of the position of equilibrium if the pressure on the reacting gases is increased

give a reason for your answer

effect = increase in product

reason = there are less atoms on the left once pressure in increased so the position of equilibrium shifts to the right to restore equilibrium

131

the reaction of heated magnesium with steam is faster than the reaction of magnesium with cold water. this is mainly because

a) in cold water, the water molecules do not collide as frequently with magnesium

b) the coating of oxide on magnesium decomposed when it is heated

c) the fraction of particles with enegry greater than the activation energy is higher in the recation with steam

d) the recation with steam gos by an alternative route (catalyst) with lower activation energy

c) the fraction of particles with enegry greater than the activation energy is higher in the recation with steam

(a and b are also correct but c is more correct)

132

This reaction is used to manufacture ammonia:

N2 + 3H2  ⇌ 2NH3

△H = -x kJ/mol

Bond N≡N has a dissociation energy (kJ/mol) of 944

Bond H-H has a dissociation energy (kJ/mol) of 436

Bond N-H has a dissociation energy (kJ/mol) of 388

calculate the energy change occuring during the reaction to manufacture ammonia

944 + (3 x 436) ⇌ 2 x (388 x 3)

2252 ⇌ 2328

2252 - 2328

= - 76

133

to obtain a reasonable yield of ammonia the reaction is carried out at a temperature of 4500C and a pressure of 250 atmospheres

predict what will happen to the yield of ammonia in the equilibrium mixture if the temperature is increased

yield will decrease

134

to obtain a reasonable yield of ammonia the reaction is carried out at a temperature of 4500C and a pressure of 250 atmospheres

predict what wil happen to the yield of ammonia in the equilibrium mixture if the temperature is increased

yield will decrease

135

the temperature of a mixture of nitrogen, hydrogen and ammonia gases is decreased until all the gases have liquefied

describe two canges in the movement of gas molecules as a gas liquefies

molecules will get closer together

molecules will lose kinetic energy (slow down)

136

molecule N2 has a heat of vaporisation (kJ/mol) of 2.8

molecule Hhas a heat of vaporisation (kJ/mol) of 0.45

molecule NH2 has a heat of vaporisation (kJ/mol) of 23

which of these gases will be the last to liquefy?

NH3

you have to take the most energy out of the NH3 gas

137

This reaction is used to manufacture ammonia in the Haber process:

N2 + 3H2  ⇌ 2NH3

△ = -92 kJ/mol

a temperature of 4500C and a pressure of 200 atmospheres are often used

if you decrease the temperature what will happen to the rate of reaction and yield of ammonia?

rate of reaction will decrease

yield of ammonia will increase

138

This reaction is used to manufacture ammonia in the Haber process:

N2 + 3H2  ⇌ 2NH2

△ = -92 kJ/mol

a temperature of 4500C and a pressure of 200 atmospheres are often used

if you add a catalyst what will happen to the rate of reaction and yield of ammonia?

rate of reaction will increase

yield of ammonia will not be affected (no change)

139

state and explain, using the kinetic theory, the effect on the rate of reaction of increasing the concentration of nitrogen in the Haber process

increases the number of particles (of nitrogen) in the system

particles collide more frequently 

increases proportion of successful collisions because of the higher rate of reaction

140

under the conditions used in the Haber process the yield of ammonia is about 15% 

what happens to the unreacted nitrogen and hydrogen?

it is reused

141

The equation for the complete combustion of methane is:

CH4 + 2O2 --> CO2 + 2H2O

the bond C-H has a dissociation energy (kJ/mol) of 412

the bond O-H has a dissociation energy (kJ/mol) of 463

the bond O=O has a dissociation energy (kJ/mol) of 496

the bond C=O has a dissociation energy (kJ/mol) of 743

use these values to calculate the energy change occuring during the complete combustion of methane

(412 x 4) + (496 x 2) --> (743 x 2) + (463 x 4)

2640 --> 3338

2640 - 3338

- 698 kJ/mol

142

the biggest error in this experiment is heat loss

suggest how the apparatus could be modified to reduce heat loss

put a lid of op

put it in an insulator - e.g. polystyrene or plastic

143

suggest why it is important to stir the chemicals thoroughly

so they react and mix and collide with each other

144

which one of these experiments was probably carried out on a different day to the others and why?

experiment 2

it has a different room temperature

145

suggest ehy experiment 4 should not be used to calculate the average change

its temperature change is anomalous

146

calculate the average temperature change from the first three experiments

(7.2 + 7.0 +6.8) ÷ 3

= 7

147

use the following equation to calculate the energy change for this reaction:

energy change in joules = 100 x 4.2 x average temperature change

100 x 4.2 x ((7.2 + 7.0 +6.8) ÷ 3)

 100 x 4.2 x 7

= 2940 J

148

in the equilibrium below, what effect would an increase in temperature have on the system (rate and yield)?

2H2S + SO2  ⇌ 3S + 2H2

△H is negative

 

increase in rate

decrease in yield

149

in the equilibrium below, what effect would an decrease in pressure have on the system (rate and yield)?

2H2S + SO2  ⇌ 3S + 2H2

△H is negative

decrease in rate

increase in yield