Reactivity 2.1 Flashcards
What do chemical reactions show about products and reactants in a reaction?
The ratio
How does the balancing of a chemical equation relate to the Law of Conservation of Mass?
No matter can be created or destroyed, so the chemical equations must be balanced i.e. atoms in reactants = atoms in products
Reactants
Elements/compounds consumed in a chemical reaction
Products
Elements/compounds produced by a chemical equation
When is a chemical equation balanced?
When atoms in reactants = atoms in products
Steps for balancing a chemical reaction
Word equation, unbalanced chemical equation, balancing, symbols of state
What is a precipitate?
An insoluble ionic compound
Ionic compounds consisting of these ions are generally soluble (no exceptions)
Na+
K+
NH4+
NO3-
CH3COO-
Exceptions to ionic compounds containing ions of Cl-, Br-, I- being generally soluble
Ag+
Pb2+
Exceptions to ionic compounds consisting of ions of SO42-, Cr2O72- being generally soluble
Pb2+
Ba2+
Ag+
Ca2+
Exceptions to ionic compounds containing CO32-, PO43- and S2- being generally insoluble
Na+
K+
NH4+
Exceptions to ionic compounds containing OH- being generally insoluble
Na+
K+
NH4+
Ba2+
Ca2+
Ionic equation
Balanced equation which only contains species that underwent change during the chemical reactions i.e. only includes species that underwent bond breaking and/or bond making
Spectator ions
Ions (liquid or aqueous) that remain unchanged during the reaction
What happens to spectator ions in an ionic equation?
Omitted
In a precipitation reaction, which ions are included in the ionic equation?
Ions that eventually end up in precipitate
Steps for writing ionic equations
Write a full chemical equation for the reaction
Show the individual ions for any species that will be present as separate ions (liquid/ aqueous ionic compounds and aqueous acids)
Eliminate any spectator ions
Write the ionic equation
Which ions are written as separate ions in an ionic equation?
Liquid and aqueous ionic compounds
Aqueous acids
Element + oxygen ->
Elemental oxide
Hydrocarbon + oxygen ->
Carbon dioxide and water
Complete combustion
Hydrocarbon + oxygen -> carbon dioxide + water
Reactive metal + water ->
Metal hydroxide + hydrogen
Acid + metal ->
Salt + hydrogen
Acid + base ->
Salt and water
Neutralisation reaction
Acid + base -> salt + water
Acid + metal carbonate ->
Salt + carbon dioxide + water
Acid + metal hydrogen carbonate ->
Salt + carbon dioxide + water
Which non-metals come in pairs?
N
O
F
Cl
Be
I
Precipitation reaction reactants
Two aqueous solutions (ions swap)
What can ionic equations be written for?
Ionisation of acids in aqueous solutions
Precipitation reactions
For a substance to dissociate into ions, it must
Be ionic or dissociate in water
Mass-mass stoichiometry
Write a balanced chemical equation for the reaction
Convert known mass to moles
Write the required mole ratio
Use the mole ratio to calculate the moles of the unknown reactant/product
Convert back to mass of unknown
Mole ratio for mass-mass stoichiometry
n(unknown) / n(known) = coefficient (unknown) / coefficient (known)
What equations can be used for mole-mole stoichiometry?
n = m / M
n = PV / RT
n = c x V
n = V / Vm (at STP)
Avogardo’s law
Equal volumes of all gases measured under the same conditions of temperature and pressure contain equal numbers of molecules
What does Avogardo’s law mean in relation to stoichiometry?
Volume-volume stoichiometry can occur, with a volume ratio found in the same way as the mole ratio
What are the assumptions when doing Volume-Volume stoichiometry?
Pressure and temperature are the same
What is the limiting reagent?
Reactant that it is totally consumed when the reaction is completed
What does the limiting reactant determine?
The theoretical amount of product produced
How to identify the limiting reactant
Balanced chemical equation for the reaction
Identify what you know about each reactant
Convert known quantities to moles
Divide the moles of each reactant by the corresponding coefficient
Smallest value is the limiting reactant. Largest value = in excess
How to predict quantity of product from limiting reactant
Use mole ratio of
n(unknown)/n(known) = coefficient (unknown) / coefficient (known)
Theoretical yield
Amount of product theoretically produced
Predicting quantity of the reactant in excess that will remain unreacted
n(excess)react / n(limiting) = coefficient excess / coefficient minting
Then,
n(excess)unreacted = n(excess)initial - n(excess)react
Percentage yield
Experimental yield / theoretical yield. X 100%
Atom economy
Molar mass of desired product / molar mass of all reactants. X 100%
Green chemistry
An approach to chemical research and engineering that seeks to minimise the production and release into the environment of hazardous substances
