Chemical Reactions Flashcards
What does the law of conservation of mass state?
In a chemical reaction, no matter is destroyed or created
What is a chemical change?
A rearrangement of the atoms in the reactants, to form the products
Why may the balance reading for the products be more than the reading for the reactants?
Gas from the air reacted with the reactants
What is the formula that links mass, moles, and Mr?
moles = mass/Mr
What is the limiting reactant?
It all reacts and limits how much product can be formed
What does it mean for a reactant to be ‘in excess’?
It does not all react, and has no affect on the amount of product formed
If the reactant molecules in a reaction have more energy in their chemical bonds than the product molecules, will energy be absorbed or released overall?
released
What is an exothermic reaction?
A reaction that releases thermal energy to the surroundings
What is an endothermic reaction?
A reaction that takes in thermal energy from the surroundings
If an exothermic reaction occurs in a closed container, what would happen to the temperature inside the container?
The temperature would increase
If an endothermic reaction occurs in a closed container, what would happen to the temperature inside the container?
The temperature would decrease
what is activation energy?
the minimum amount of energy the reactant particles require in order to collide successfully with each other and react.
On reaction profile diagrams, what is the activation energy?
the increase in energy from the reactants to the peak of curve.
Does breaking bonds release energy or require energy?
require
Is breaking bonds exothermic or endothermic?
Endothermic
What is bond energy?
the amount of energy required to break one mole of a particular covalent bond.
Is forming a bond an exothermic or endothermic process?
exothermic
How do you calculate the overall enthalpy change of a reaction?
(energy of) bonds broken - (energy of) bonds formed
What type of reaction produces a negative energy change?
An exothermic reaction
What does the pH scale measure?
acidity or alkalinity of a solution
What pH does stomach acid typically have?
about 2
What are 2 ways to measure the pH of a solution?
Chemical indicator
pH probe
What ion is responsible for making a solution alkaline when it’s dissolved in it?
OH -
Which products are formed when an acid reacts with a metal oxide?
a salt and water
What type of reaction is it when an acid and a base react together?
Neutralisation reaction
Which products are formed when an acid reacts with a metal hydroxide?
a salt and water
Which products are formed when an acid reacts with a metal carbonate?
a salt, water and carbon dioxide
How do you obtain soluble salt crystals from an acid-base reaction?
1)Place dilute acid in a beaker and heat gently.
2)Add the solid base bit by bit until it stops reacting, which means it’s in excess.
3)Isolate the salt solution by filtering out the excess solid base using filter paper and a funnel.
4)Heat the salt solution gently in a water bath until crystals start to form.
5)Let the solution cool further, which will cause more crystals to precipitate.
6) Filter out the soluble salt crystals using filter paper and funnel.
What does it mean when an acid ionises?
when the acid molecules are added to water, they split apart
Whats the difference between a strong and a weak acid?
Strong acids ionise completely, whereas weak acids only partially ionise.
What are 3 strong acids?
Nitric acid
Sulfuric acid
Hydrochloric acid
is the ionisation of weak acids reversible?
yes
What are 3 weak acids?
carbonic
ethanoic
citric
As the concentration of hydrogen ions in a solution increases, what happens to the pH?
The pH decreases
A solution decreases from pH 6 to pH 5.
By what factor has the concentration of hydrogen ions increased?
x10
With respect to electrons, reduction is:
The gain of electrons
With respect to electrons, oxidation is:
the loss of electrons
What is a spectator ion?
an ion that doesn’t take part in the reaction and so keeps the same charge
An electrolysis cell has two electrodes. What is the name of the positive electrode?
anode
An electrolysis cell has two electrodes. What is the name of the negative electrode?
cathode
What is the name of the liquid the electrodes are put in?
electrolyte
In electrolysis, which direction do the electrons travel?
Anode ➔ Cathode
What does the term ‘inert’ mean?
unreactive
In the electrolysis of molten lead bromide, what is the product at the anode?
bromine
In electrolysis, why does the compound you’re trying to separate need to be molten or dissolved?
So that the ions are free to move around (and go to their respective electrode)
Which 2 chemical processes are used to extract metals from their ores?
reduction with carbon and electrolysis
What is electrolysis?
the splitting of an ionic compound using electricity
Why is electrolysis not used to extract all metals?
Electrolysis is expensive because it requires a large amount of electricity
When should a metal be extracted by carbon reduction?
When the metal is less reactive than carbon
Why is electrolysis used to extract aluminium from its ores?
it is more reactive than carbon
What is the name of the substance that is mixed with aluminium oxide to lower its melting point?
cryolite
In the electrolysis of a solution, which two ions are present from the water molecules themselves?
H+ OH-
What is the rule to determine which ion get discharged at the cathode in aqueous electrolysis?
the ions of the least reactive metal will be discharged (usually copper or hydrogen)
What is the rule to determine which ion get discharged at the anode in aqueous electrolysis?
If halide is present, it gets discharged, otherwise hydroxide gets discharged
