Flashcards in Module 3 Deck (86):
What is the first ionisation energy?
The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
What are the factors affecting ionisation energy?
• the greater the distance between the nucleus and the outer electrons the less the nuclear attraction
• the more proton there are in the nucleus of an atom the greater the attraction between the nucleus and the outer electrons
• inner shell electrons repel outer shell electrons
What is the second ionisation energy?
The energy required to remove one electron from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Trends in first ionisation energies
General increase across each period
Sharp decrease between the end of one period and the start of the next period
Decrease down a group
Trends across a period
Nuclear charge increases
Nuclear attraction increases
Atomic radius decreases
First ionisation energy increases
What is metallic bonding?
The strong electrostatic attraction between actions and delocalised electrons
What happens in metallic bonding?
Each atom has donated its outershell electrons to a shared pool of electrons which are delocalised.
The cations left behind consist of the nucleus and the inner electron shells of the metal atoms.
Properties of metals
Strong metallic bonds
High electrical conductivity
High melting and boiling points
What are giant covalent lattices?
Many billions of atoms held together by a network of strong covalent bonds
What is the bond angle in a giant covalent lattice?
Properties of giant covalent lattices
High melting and boiling points
Insoluble in almost all solvents
Only graphene and graphite are able to conduct electricity
What is the periodic trend in melting points?
• melting point increases from group 1 to group 14
• sharp decrease in melting point between group 14 to 15
• comparatively low melting points from group 15 to 18
What is a reducing agent?
An element that has reduced another species and has been oxidised itself
Are group 2 metals oxidising agents?
No. They are reducing agents
What is formed when a group 2 element reacts with oxygen?
A metal oxide with the general formula MO
What is formed when a group 2 element reacts with water?
An alkaline hydroxide, with the general formula M(OH)2, and hydrogen gas
Metal + acid =
Salt + hydrogen
What is the reactivity trend down group 2?
Reactivity increases down the group
What is formed when a group 2 oxide reacts with water?
Hydroxide ions are released forming alkaline solutions of the metal hydroxide
What is the trend in solubility of hydroxides in water?
Increases down the group
The resulting solutions contain more OH- ions and are more alkaline
What can group 2 compounds be used for?
• calcium hydroxide, Ca(OH)2, is added to fields to increase the soil Ph
• used as anti acids for treating acid digestion
What do halogens exist as?
Trends down group 7(the halogens)
Stronger London forces
Boiling point increases
What is the most common type of reaction of the halogens?
Are halogens oxidising agents?
Yes, they oxidise another species
How does reactivity change down group 7?
Reactivity of halogens decreases down the group
For displacement of halogens, a solution of each halogen is added to aqueous solutions of the other halides. What happens if the halogen added is more reactive than the halide present?
• a reaction takes place, the halogen displaces the halide from solution
• the solution changes colour
Colour of Cl2+Br-
Orange from Br2 formation
Colour of Cl2+ I-
Violet from I2 formation
Colour of Br2 + I-
Violet from I2 formation
Colour of Cl2
Colour and state of fluorine
Pale yellow gas
What is a disproportionation reaction?
A redox reaction in which the same element is both oxidised and reduced
How do you test for carbonates?
Add dilute nitric acid
If you see bubbles it could be a carbonate
Bubble the gas through lime water (calcium hydroxide, Ca(OH)2
CO2 reacts to form a white precipitate if calcium carbonate which turns the limewater cloudy
How to test for sulfates
Add Ba2+ ions as barium chloride or barium nitrate
(Use barium nitrate if you plan to carry out a halide test afterwards)
A white precipitate of barium sulfate, BaSO4, is formed
How to test for halides
Add aqueous silver nitrate, AgNO3
White precipitate : silver chloride
Cream precipitate : silver bromide
Yellow : silver iodide
Add aqueous ammonia to test the solubility
Cl- : soluble in solute NH3
Br- : soluble in conc NH3
I- : insoluble in conc NH3
Are bromide ions soluble in dilute NH3?
No, they are soluble in concentrated NH3
Are iodide ions soluble in dilute NH3?
No, they are not soluble in conc NH3 either
What order should the tests for anions be carried out?
How do you test for ammonium ion, NH4?
Add aqueous sodium hydroxide, NaOH
Ammonia gas is produced
The mixture is warmed and ammonia gas is released
Indicator paper will turn blue
What is enthalpy?
A measure of the heat energy is a chemical system
Often thought of as the energy stored within bonds
Cannot be measured however enthalpy changes can
How do you calculate the enthalpy change?
/\H = H(products) - H(reactants)
What is an exothermic reaction?
Energy transfer from the system to the surroundings
/\H is negative
The chemical system loses energy
What is an endothermic reaction?
Energy transfer from the surroundings to the system
/\H is positive
Chemical system gains energy
What type of reaction has a negative /\H?
An exothermic reaction
Does an endothermic reaction have a negative /\H?
No, /\ H is positive for endothermic reactions
What is activation energy?
The minimum energy required for a reaction to take place
What is the standard enthalpy change of reaction?
The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all products and reactants in their standard states
What is the standard enthalpy change of formation?
The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all products and reactants in their standard states
What is the enthalpy change of formation for an element?
What is the standard enthalpy change of combustion?
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all products and reactants in their standard states
What are the products when a substance reacts completely with oxygen?
The oxides of the elements in the substance
What is the standard enthalpy change of neutralisation?
The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O under standard conditions, with all products and reactants in their standard states
How do you calculate an energy change?
What is the specific heat capacity of a substance?
The energy required to raise the temperature of 1g of a substance by 1K
Why is enthalpy change of combustion calculated to be more than the actual value?
Heat loss to surroundings
What is the average bond enthalpy?
The energy required to break one mole of a specified type of bond in a gaseous molecule
In what type of reaction are bonds broken?
What happens to the bonds in an exothermic reaction?
The bonds are formed
How do you calculate average bond enthalpies?
Sum of bond enthalpies in REACTANTS - sum of bond enthalpies in PRODUCTS
What is Hess’ law?
If a reaction can take place by two routes, and the starting and finishing conditions are the same, the total enthalpy change is the same for each route
Calculating enthalpy changes of formation
Sum of enthalpy changes of PRODUCTS - sum of enthalpy changes of REACTANTS
Calculating enthalpy changes of combustion
Sum of REACTANTS - sum of PRODUCTS
How do you calculate rate?
Change in concentration / time
What factors can affect the rate of a chemical reaction?
Use of a catalyst
What is the collision theory?
Two reacting particles must collide for a reaction to occur
Under what conditions will a collision be effective?
The particles collide with the correct orientation
The particles have sufficient energy to overcome the activation energy
What does a catalyst do?
Changes the rate of a chemical reaction with out undergoing any permanent change itself
Produces an alternative pathway to lower the activation energy
What is a homogeneous catalyst?
Has the same physical state as the reactants
What happens in an equilibrium system?
The rate of the forward reaction is equal to the rate of the reverse reaction
The concentration of reactants and products do not change
What is Le Chatelier’s principle?
When a system in equilibrium is subjected to an external change the system adjusts itself to minimise the effect of that change
What happens to an equilibrium when there are more products formed?
The position shifts to the right
What happens when the concentration of the reactants in equilibrium increases?
Equilibrium shifts right
What happens when the concentration of the products are increased in equilibrium?
The equilibrium position shifts left
Where does the equilibrium shift when the temperature is increased?
Shifts in the endothermic direction (/\H is positive)
What has happened to the temperature when the equilibrium shifts towards the exothermic direction?(/\H is negative)
Temperature has decreased
What must be true for a change in pressure to affect the direction of equilibrium?
All products and reactants must be gases
What will happen to the equilibrium position when pressure is increased?
The equilibrium will shift towards the side with fewer molecules
How would pressure change if the equilibrium has been shifted to the side with the most molecules?
Pressure will have decreased
How does a catalyst effect the position of equilibrium?
It has no change, it only speeds up the rates of both sides equally
How do you calculate the equilibrium constant? Kc
Kc = [products] / [reactants]
What does a larger value of Kc mean for the position of equilibrium and the concentrations?
The position of equilibrium is further to the right
Concentrations of products are greater compared to the reactants
What type of catalyst has a different chemical state from from the reactants?
In what state are heterogeneous catalyst usually used in?
Solids in contact with gaseous reactants or reactants in solution
Reactant molecules are absorbed into the surface of the catalyst and leave the surface after the reaction by desorption
What Kc values indicate a position of equilibrium towards the products?
Kc > 1