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chemistry igcse > Chapter 7 > Flashcards

Chapter 7 Flashcards

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1
Q

Reversible reactions

A
  • The physical and biological world is the product of a complex set of chemical interactions and reactions
  • some reactions can be reversed if we exchange the conditions
  • the reversible hydration of salts by thermal decomposition to give dehydration of the salts
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2
Q

The concept of equilibrium

A
  • Chemical equilibrium occurs when a reaction and it’s reverse reaction proceed at the same rate
  • only get an equilibrium with a closed system (reversible reaction)
  • as a system approaches equilibrium, both the forward and reverse reaction occurring at the same rate
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3
Q

The equilibrium constant

A

The ratio of the rate constant is a constant (as long as temp is constant)

Keq = KF/Kr

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4
Q

Le chateliers principle

A

If a system at equilibrium is disturbed by a change in temp, pressure or in concentration at one of the components, the system will shift has to a equilibrium position so as the countered the effect of disturbance

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5
Q

Condition that affects a chemical equilibrium

A
  • temp
  • concentration
  • pressure

-catalyst has no effect on position of chemical equilibrium but the reactions reaches equilibrium faster and

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6
Q

Condition for Harber Process manufacture of NH3

A

Condition that affects a chemical equilibrium

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7
Q

Pressure

A

High pressure = low volume
Low pressure =high volume
-Equilibrium moves towards reactants side when high pressure

•~•position shift= more no miles to fewer no of moles

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8
Q

The contact process - making sulfuric acid

A

The conditions used in the contact process

  • an optimum temp of about 450 is chosen
  • a catalyst of Vanadium (v) oxide is used
  • an operating pressure of about 1 atm has a applied
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9
Q

Uses of h2so4

A
  • fertilizers
  • superphosphate of lime/drugs
  • ammonium sulphate/explosives
  • manufacturing of hydrochloric acid
  • dyes and pigments
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10
Q

Weak acids and alkali

A

Dynamic equilibrium are set up in solution of weak acids and weak alkalis because these molecules are only partially dissociated in ions in water

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11
Q

Redox reactions

A

Red-reduction (loss of electrons)
Ox-oxidation (gain of electrons)

This reaction - involves transfer of electrons from the reducing agent to the oxidizing agent

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12
Q

Oxidation

A

Is the increase in oxidation number state of an atom or ion

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13
Q

Reduction

A

Is the decrease in oxidation number state of an atom or ion

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14
Q

Reducing agent

A

Electron donor or atom/ion that was oxidized

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15
Q

Oxidizing agent

A

Electron acceptor or atom/ion that was reduced

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16
Q

Test for oxidizing agents

A

-Reactions involving KI very useful as a test for oxidizing agents ,became a Coloured change is produced
•I^- is oxidized for I^2. The Coloured or the solution changes from colorless to yellow-brown. If starch indicator is added, then a dark blue Coloured is produced

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17
Q

Test for reducing agent

A

Reactions involving potassium manganese (VII) are useful for detecting a reducing agent. Reduced from MN^+7 (purple Colour) to which appears colorless because of the formation of pale pink Mn^+2 ions

18
Q

Electrolysis

A
  • process by which electric current is passed through a substance to cause a chemical change
  • the chemical change is one in which substances loses or gains an electron
19
Q

Electrolysis def

A

Electrolysis is the break down of an ionic compound, molten or in aqueous solution, by the use of electricity

20
Q

Setup for electrolysis experiment

A
  • the process uses an apparatus consisting of positive and negative electrode which are separated from each other in a solution
  • electric current enters through the negativity charged electrode(cathode)
  • positivity charge parts of the dilution travels to the cathode combines with the electrode, and are transformed into neutral molecules
  • The negativity charged parts of the solution travel to positive electrode(anode) give up electron
21
Q

Conductivity in solids - conductors and insulators

A
  • all metals conduct electricity but carbon in the form of graphite is the only non metal conductor
  • metals (and graphite) conduct electricity because they have free mobile electrons in their structure
  • solid covalent non-metal do not conduct electricity
  • there is no chemical change when an electric current is passed through a metal or graphite. The copper wire is still copper when current is switched off
  • electrical conductor: a substance that conducts electricity but is not chemically changed in the process
22
Q

Two distinct types of electrical conductivity (their difference )

A

Metallic and electrolytic conductivity

23
Q

Metallic conductivity

A

Electrons flow, property of elements (metals and graphite) and alloys, takes place in solids and liquids, no chemical change takes place

24
Q

Electrolytic conductivity

A

Jon’s flow, a property of ionic compounds, takes place in liquids and solution (not solid) , chemical decomposition takes place

25
Q

Supplying electricity

A
  • electricity is transmitted along power cables made from copper because of its properties: good conductor
  • over head power cables are made from aluminum because of ; good conductor, low density, resistance to corrosion
  • domestic cables are covered in plastic for safety
  • leakage of power from overhead cables is prevented by using ceramic materials between the cables and the plums
26
Q

Conductivity by liquids

A

Instead of dipping some materials to be tested into liquid circuit, graphite rods are dipped into the test liquid l. Liquids compounds, solutions are molten material can be tested in this way

  • •electrolytes : liquids that conduct electricity by movement of ions are called electrolyes
  • •liquids that do not conduct electricity in this way are called non-electrolytes
27
Q

The movement of ions

A

The conductivity of ionic compounds is explained by the fact that ions move in a particular direction an electric field
-electrodes are rods (graphite) that carry current into and out of the solution

28
Q

The electrolytic cell

A

The apparatus in which electrolysis is carried out is known as an electrolytic cell

  • the direct current (DC) is supplied by a battery or power pack
  • graphite electrodes Garry that current into and out of the liquid electrolyte. Graphite is chosen because it is quite un-reactive
  • electrons flow from negative terminal to positive terminal around the circuit
  • in the electrolyte is the ions that move to carry the current
29
Q

At the cathode

A

The more reactive a metal, the more it tends to stay as ions and not be discharged. The H+ ions will accept electrons instead and hydrogen molecules will be formed, leaving the ion at the reactive ions eg: not ions in solution ( compare between CU2+ (less reacted) and (H*+)

30
Q

Electrolysis has f concentrated NACL solution (four different ions present in solution)

A
  • Na+ and H+ flow to the cathode. But It is H*+ that affects electrons as sodium is made reactive than hydrogen
  • then the 2 hydrogen the atoms combine liquid to form a hydrogen molecule
  • so the overall, hydrogen gas bubble off at the cathode
  • Cl- and OH- travel to the anode. CL- ions are discussed more readily than OH-
31
Q

Acid solutions electrolysis

A

Pure water (bad conductor) + acid

  • an example of electrolytic cell use for electrolysis Of brine
  • it is the safest for the environment and uses the least electricity
  • other types of cell use either a flaming mercury cathode or a discharged (partition ) made from asbestos
  • titanium’s chosen for the anode as it is not affected by chlorine
  • a membrane separated the anode and cathode components. This membrane is selective because it only allows Ana ions and water to flow through but no other ions
  • this means product are kept separate and cannot react with each other
  • the Na*+ and OH- ions collect in the cathode compartment
  • the NAOH solution is removed and purified
32
Q

Electroplating

A
  • can being def to coast one metal with another
  • cathode is the object to be played and the anode is made from the metal being used to plate it
  • the electrolyte is a salt of the same metal-as the process proceeds, the anode dissolved away into the solution replacing the metal plated onto the object
  • and the concentration of solution remains the same
  • most commentary used metals use for electroplating are copper, chromium, silver and tin
  • electroplating give a protective coating to the metal underneath
  • also attractive appearance
  • nickel silver is an alloy of copper, zinc and nickel. It contains no silver at all. (EPNS) meaning electroplated nickel silver :33’ on cutlery and other objects
33
Q

Reversible reactions

A

Under same conditions in a closed system, the products can interact to reverse the reaction

Used in industry for the reaction between niytogen and hydrogen to produce ammonia
N2 + 3H2 2NH3 is that

34
Q

Fritz Haber

A

Was the first to show this reaction could be controlled to make useful amounts of ammonia.now known as the Haber Process

35
Q

Reversible hydration of salts

A

Thermal decomposition of salts such as hydrated copper 2 sulfate results in the dehydration of the salt

CuSO4.5H2O —-> CuSO4 + 5H2O

(Some reactions for example dehydration or hydrate salts can be reversed if the conditions are changed)

36
Q

The Haber process

A

Making ammonia
Forward reaction:
n2 + 3H2 -> 2NH3

Reverse reaction:
2NH3 -> N2 + 3H2

37
Q

Le Chateliers principle

A

Dynamic equilibrium- a state of balance between continuing processes.
It also states: when a change is made to the conditions of a system when a change is made to the conditions or a system in dynamic equilibrium, the system moves so as to oppose that change

38
Q

Reversible reactions is in equilibrium when

A
  • the rates of the forwards and reverse reactions are equal
  • the concentrations of reactants and products do not change
  • concentrations for a particular reaction depend on the conditions used. Changing temp alters the equilibrium position. Changing the working pressure can also alter the equilibrium position for some reactions involving gasses
  • a catalyst does not alter the equilibrium concentrations of reactants and products, it does increase the rate at which equilibrium is reached
39
Q

Conditions of Haber Process

A
  • N2 and H2 are mixed in a ratio of 3:1
  • an optimum temp of 450 is chosen
  • A pressure of 200 atm
  • catalyst final divided iron is used
  • the ammonia is condensed out of the reaction mixture and the remaining N2 and H2 is recycled
40
Q

Condition

A
  • catalyst -does not affect the position of equilibrium but at rate
  • temp - increasing makes reaction move in the direction that takes in heat (endothermic direction
  • concentration -increasing makes equilibrium move in the direction of that produces less of that substance
  • pressure -only affects reactions with gas, increasing shifts the equilibrium in the direction that produces fewer gas molecules
41
Q

Contact process

A

Manufacturing of sulfuric acid, converts sulfur dioxide(SO2) to sulfur trioxide (SO3) is reversible

Exothermic and is favored by low

  • optimum temp of 450
  • a catalysis or vanadium (v) oxide
  • operating pressure of about 1atm

chemistry igcse (9 decks)

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