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chemistry > 6 - Chemical Reactions > Flashcards

6 - Chemical Reactions Flashcards

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1
Q

Def. Oxidation - 18th Century definition

A

The gain of oxygen of a substance

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2
Q

Def. Reduction - 18th Century definition

A

The loss of oxygen of a substance

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3
Q

Def. Oxidation - 20th Century definition

A

The loss of electrons

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4
Q

Def. Reduction - 20th Century definition

A

The gain of electrons

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5
Q

Def. Redox Reaction

A

A reaction where Oxidation and Reduction occur simultaneously

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6
Q

What does the OILRIG mnemonic stand for?

A
  • O xidation
  • I s
  • L oss of electrons
  • R eduction
  • I s
  • G ain of electrons
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7
Q

What can be said about Oxidation and Reduction in terms of relationship

A

Oxdation cannot happen without reduction and vice versa as if an element gains electrons, another must lose them to balance the reaction out

Electrons cannot be created nor destroyed

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8
Q

What is an oxidation number?

A

The number of electrons lost or gained by an atom of an element

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9
Q

What is the first rule concerning oxidation numbers?

A

The oxidation number of elements in their combined state is zero.

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10
Q

What is the second rule concerning oxidation numbers?

A

The oxidation number of a monoatomic ion is the same as the charge on the ion

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11
Q

What is the third rule concerning oxidation numbers?

A

The sum of the oxidation numbers in a compound is always zero.

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12
Q

What does it mean if the oxidation number of substance increases throughout a reaction?

A

Oxidation has occured

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13
Q

What does it mean if the oxidation number of substance decreases throughout a reaction?

A

Reduction has occured

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14
Q

What is a fast way to know if a reaction is redox without calculating Oxidation number changes?

A

If an element becomes a compound and vice versa, the equation is a redox reaction.

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15
Q

How do you use oxidation numbers to understand which element/ion/compound has been reduced or oxidated?

A

You figure out the oxidation nuber of an atom, then compare the change from the reactants to the prodcts.

Increase in result is oxidation. Decrease in result is reduction.

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16
Q

What is an ionic equation?

A

An equation that shows the species (species refers to an atom, molecule, or ion that takes part in a chemical reaction) involved in the reaction and does not include spectator ions

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17
Q

What is the difference between species and spectator ions?

A

Species refers to an atom, molecule, or ion that takes part in a chemical reaction, while spectator ions don’t make bonds, or lose or gain electrons, or react in general.

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18
Q

What aspects of equations are broken up to turn them into ionic equations

A

Ionic compounds only. Elements and covalent compounds should not be removed

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19
Q

How do you turn an equation into an ionic equation?

A
  1. Break the ionic compounds into seperate ions
  2. Remove all ions that do not undergo oxidation or reductions throguhout the reaction (spectator ions)
  3. Reasemble the equation together
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20
Q

What is the difference between ionic equations and ionic half equations?

A

Ionic half equations only represent one ion and shows electrons while ionic equations do not display electrons at all and include different ions, covalent molecules and elements

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21
Q

What colour is an Iodide ion? (I-)

A

Colourless

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22
Q

What colour is iodine? (I2)

A

Red/brown

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23
Q

Def. Oxidating Agent

A

A substance that oxidises another substance and is itself reduced

It steals electrons from the atom it oxidises

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24
Q

Def. Reducing agent

A

A substance that reduces another substance and is itself oxidised

It gives away electrons to the atom it reduces

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25
Q

What colour is the Manganate ion? (MnO4-)

A

Purple

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26
Q

What colour is the Manganese ion? (Mn2+)

A

Colourless

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27
Q

What Physical changes occur in a candle?

A
  • Wax melting
  • Wax solidifying
  • Wax evaporating
  • Wax softening
  • Air particles vibrate faster
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28
Q

What chemical changes occur in a candle?

A
  • Combustion of wax
  • Smoke formed
  • Combustion of wick
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29
Q

Def. Physical changes

A

A change in which no new substances are formed, particles remain the same

e.g dissolving or state changes

30
Q

Def. Chemical change

A

A change in which a new substance is formed

e.g Chemical reaction like combustion

31
Q

On a graph, what mathematical concept is the rate of reaction equal to?

A

The gradient of a line

32
Q

Give a graph, how do you find the rate of reaction?

A

Rate of Reaction = Δy/Δx

33
Q

Give an example of the rate of reaction formula

A

Rate = Δmass/Δtime

measured in g/s

34
Q

What are the products of the reaction between sodium and water?

A

Hydrogen and sodium hydroxide

35
Q

Describe the rate of reaction of a substance reacting when it gives of a gas

A

The rate of reaction at first is fast (steep gradient) to start with, but then slows down (shallow gradient)

36
Q

Def. Independent Variable

A

The variable that is changed during an experiment

37
Q

Def. Dependent Variable

A

The variable that is measured during an experiment

38
Q

Def. Control Variables

A

The variables that are kept the same during a chemical reaction

39
Q

What are the 5 ideas of Collision Theory?

A
  1. Particles must collide in order for a reaction to occur
  2. Particles require minimum energy, the activation energy, in order to break their bonds and react
  3. If particles have sufficient energy, then the collision will be successful
  4. Not all collisions are successful
  5. In order to increase the rate of reaction, we must increase the chance of a successful collision
40
Q

Use collision theory to explain why an increase in surface area leads to an increase in rate of reaction

A
  • Smaller chips have a bigger surface area so more particles are exposed
  • This means that collisions are more frequent/there are more collisions per second
  • Therefore there is a higher frequency of successful collisions
41
Q

Use collision theory to explain why an increase in pressure leads to an increase in rate of reaction

A
  • The pressure causes particles to be forced closer together
  • This means that collisions are more frequent/there are more collisions per second
  • Therefore there is a higher frequency of successful collisions
42
Q

Use collision theory to explain why an increase in acid concentration leads to an increase in rate of reaction

A
  • The higher concentration means that there are more acid particles per unit volume
  • this means collisions are more frequent
  • Therefore there is a higher frequency of successful collisions
43
Q

Use collision theory to explain why an increase in temperature leads to an increase in rate of reaction

A
  • The particles in high temperature have higher energy that cold ones
  • This means that a greater proportion of the collisions have the activation energy needed for a successful collison, and due to the increase in energy of the particles, they will also move faster and there will be more collisions per second
  • Therefore there is a higher frequency of successful collisions
44
Q

Use collision theory to explain why the use of a catalyst leads to an increase in the rate of reaction

A
  • The catalyst reduces the activation energy needed for a successful collision
  • More particles possess the energy needed for a successful collision
  • Therefore there is a higher frequency of successful collisions
45
Q

Why is freezing a good way of preserving food?

A
  • The temperature is lowered, resulting in a decrease of energy for each particle, so a smaller proportion of the particles have the activation energy required for a successful collision.
  • Frozen particles will vibrate on the spot instead of moving around due to their lack of energy, drastically reducing the number of collisions
  • Therefore here is a lower frequency of succesful collisions
46
Q

What are reversible reactions?

A

Reactions where the products can return and become the reactents once again

47
Q

Compare the reversibility of physical vs chemical changes

A
  • Physical changes are usually reversible
  • Only some chemical changes are reversible
48
Q

What factors can you tweak to change the rate of reaction of a metal reacting with an acid?

A
  • Temperature
  • Surface area
  • Type of metal used
  • Concentration of acid (in Moles)
  • Amount of reactants used
  • Pressure
49
Q

What can be deduced if a reversible reaction is exo/endothermic?

A

The reaction occuring the other way down will be the opposite e.g. if one way, it is endothermic requires 30J of energy, the other way it will be exothermic and release 30J

50
Q

Compare hydrated and anhydrous salts

A

Hydrated salts are bonded with water molecules while anhydrous salts have no water

51
Q

What are the characteristics of chemical equilibrium?

A
  1. The reversible reaction must be in a closed system
  2. The forward and backward reactions occur at the same rate
  3. The concentration of the reactants & products stays the same
52
Q

What is the position of equilibrium if the proportion of reactants in a reversible reaction is greater than the proportion of the products?

A

Equilibrium is on the left

53
Q

What is the position of equilibrium if the proportion of reactants in a reversible reaction is equal to the proportion of the products?

A

Equilibrim is in the middle

54
Q

What is the position of equilibrium if the proportion of reactants in a reversible reaction is smaller than the proportion of the products?

A

Equilibrium is on the right

55
Q

Def. Position of Equilibrium

A

The proportion of reactants & products at equilibrium

56
Q

What is Le Chatelier’s Principle?

A

Whenever a system is subjected to a change, a reaction will occur to oppose the change and return to equilibrium

57
Q

What are the four conditions that affect the rate of reaction in reversible reactions?

A
  • Temperature
  • Proportion of reactants to products
  • Pressure, if the reaction is gaseous
  • Catalysts
58
Q

Explain the effects of temperature on the equilibrium of a reversible reaction according to Le Chatelier’s principle

A

If temperature is increased, the endothermic reaction will occur to reduce the temperature and the equilibrium will shift in the direction of this reaction. Likewise, if the temperature decreases, an exothermic reaction will occur.

59
Q

Explain the effects of the proportion of reactants and products on the equilibrium of a reversible reaction according to Le Chatelier’s principle

A

If more reactants are added, the forward reaction will occur to reduce the concentration of the reactants and restore the pressure. The position of equilibrium therefore moves to the right.

And, of course, vice versa

60
Q

Explain the effects of the pressure on the equilibrium of a gaseous reversible reaction according to Le Chatelier’s principle

A

For gaseous reactions ONLY - If the pressure is increased, a reaction will occur to decrease the number of moles of gas and therefore reduce the pressure. The position of equilibrium moves to the side with less moles of gas.

And, of course, vice versa

61
Q

Explain the effects of a catalyst on the equilibrium of a reversible reaction according to Le Chatelier’s principle

A

A catalyst speeds up both the forward and backward reactions equally and therefore does not affect the position of equilibrium. However, it is useful to speed up reactions such as the haber process where the products are constantly being removed.

Important - The position does not change

62
Q

What is the balanced chemical reaction for the Haber process?

A

N2 + 3H2 ⇌ 2NH3

63
Q

Describe the steps of the Haber Process

A
  1. The reaction CH4 + 2H2O → CO2 + 2H2 is used to produce hydrogen, and Nitrogen is extracted from the air
  2. These get forced to a pressure of 200 atm to get optimum percentage yield of ammonia
  3. Iron catalyst beds are used to speed up the reaction which produces ammonia, so it is produced faster
  4. The ammonia is removed during the process by beng cooled to -10 degrees by a cooling tank
  5. The Nitrogen and Hydrogen which did not react, the majority, is recycled back to make the reaction occur again and not be watsted

To give an idea, this process has a 15% yield

64
Q

What reaction is used to produce Hygrogen for the Haber process?

A

CH4 + 2H2O → CO2 + 2H2

65
Q

Explain why the 200 atm of pressure in the haber process results in an optimum yield of ammonia

A

The very high pressure, 200 atm, causes the position of equilibrium to move to the side of the reaction with less moles. This is ammonia, which has only 2 moles compred to the 4 moles of Hydrogen nánd Nitrogen on the other side. Therefore there is a higher yield of ammonia.

66
Q

Explain why the relatively high temperature, 450 degrees in the haber process results in an optimum yield of ammonia

A

A temperature that would be too high would favour the endothermic backward reaction, but any temperature below 450 degrees would result in the haber process occuring too slowly (which is not economically favourable) because the particles do not have enough activation energy.

67
Q

Explain why the Iron Bed catalysts in the Haber Process result in an optimum yield of ammonia

A

The catalyst speeds up bothe the forward and backward reactions so the equilibrium does not change, but ammonia is produced and can be therefore removed more quickly

68
Q

What is the symbol equation for the conversion of sulfur dioxide to sulfur trioxide?

In the contact process

A

2SO2 (g) + O2 (g) ⇌ 2SO3 (g)

69
Q

What are the sources of sulfur dioxide?

A
  • Combustion of sulfur
  • Roasting sulfite ore with oxygen
70
Q

What are the necessary conditions for the contact process?

A
  • 450 degrees Celsius
  • 2atm/200kPa
  • Vanadium (V) Oxide Catalyst
71
Q

Why are catalysts used in the Haber and Contact processes?

A
  • Efficiency - The catalyst speeds up the reaction so more of the product can be removed
  • Economy - Using a catalyst is less expensive than increasing other conditions such as pressure
  • Safety - A catalyst is safer to use that an increased pressure

chemistry (12 decks)

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