G10 CHEM Flashcards
Reversible reactions
Both forward and the reverse reaction can occur as the product molecules can themselves react with each other or decompose and form the reactant molecules again
If the forward reaction is exothermic, the reverse will be
endothermic as the same amount of heat is transferred in both direction
Equilibirum
A system is said to be in equilibrium when the rate of forward reaction is equal to the rate of the backward reaction and the concentration of reactant and product becomes constant in a reversible reaction in a close system
More product than reactant,
Equilibrium lies to the right
More reactant than product
Equilibrium lies to the products side
Types of equilibrium
Physical and Chemical
Physical equilibrium
If there is a physical change and only the state changes
Chemical equilibrium
If there is a chemical change and new substance is formed
Example of physical equilibrium reaction
Any hydrated salt breaking down into anhydrous salt + water
Le chatelier’s principle
When a system in equilibrium is disturbed, the equilibrium wants to undo the disturbance to go back to equilibrium
What are the factors affecting equilibrium
Temp
Pressure
Concentration
Catalyst
How does a change in temperature affect the equilibrium
Increasing the temperature shifts the equilibrium to endothermic side
Decreasing the temperature shifts the equilibrium to the exothermic side
How does a change in the pressure affect the equilibrium
Increase in pressure means no of particles per unit volume increase and hence equilibrium wants to go to side with less particles. Decreasing the pressure means the equilibrium will shift to the side with more gas molecules. This is because reducing the pressure makes the system want to occupy more volume
3H_2 + N_2 ⇌ 2NH_3
where will the equilibrium shift
3 + 1 = 4 > 2
Hence equilibrium will shift in forward direction, increasing the yield of ammonia
How does a change in the concentration affect the equilibrium
Increasing the concentration of reactants/Decreasing concentration of products = equilibrium shifts in forward direction
Increasing concentration of products/Decreasing concentration of reactant = equilibrium shifts in reverse direction
How does adding a catalyst affect the equilibrium
Add a catalyst = increase rate of forward reaction and backward reaction in the same manor
Adding catalyst means equilibrium will be achieved faster, but they will have no effect in the yield of products/reactants
In an equilibrium graph, what happens to the lines of rate of forward and reverse reaction
The line representing rate of forward reaction gradually decreases before becoming constant
The line representing rate of reverse reaction gradually increase before becoming constant
What is the region called where the rate of forward and backward reactions are not constant, ie the region before equilibrium
Kinetic region
Haber’s process
industrial method for ,making ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂) gases at high pressure, moderate temperature and with a catalyst
Why is Haber process important in daily life
Haber process makes ammonia, which is an essential ingredient in the production of fertilisers, which helps grow the crops we eat
Redox Reaction
A reaction where oxidation and reduction both happen simultaneously
Conditions for oxidation to happen
1) gain of oxygen
2) Loss of electrons
3) Loss of hydrogen atoms
4) Increase in oxidation number
conditions for reduction to happen
1) loss of oxygen
2) gain of electrons
3) gain of hydrogen atoms
4) decrease in oxidation number
Who will undergo oxidation or reduction
Only reactants
Reactant which oxidises
Reductant/Reducing agent
Reactant which is reduces
Oxidizing Agent/Oxidant
4 main properties to remember to convert molecular equations into ionic equations
Solids, liquid and gases cant disassociate into ions
only aqueous solutions will disassociate
Solids always lose electrons
Aqueous will always gain electrons
atoms in free state oxidation no
0
oxidation number of group 1 elements in all its compounds
+1
oxidation number of group 2 elements in all its compounds
+2
oxidation number of oxygen in all its compounds
-2
oxidation number of group 7/17 elements in all its compounds
-1
oxidation number of hydrogen in all its compounds
+1
Oxidation number of monoatomic ions
change present on the ions
Sum of oxdiation numbers in a compounds is equal to
0
Sum of oxidation number in a polyatomic ion is equal to
charge present on ion
what happens in rusting and corrosion in terms of redox reactions
metal is oxidized (loses electrons), and typically oxygen is reduced (gains electrons)
All nitrates and sulphates are…
soluble in water
colour of copper salt
blue, shade depends on centration of salt of copper present
Reactivity series of metals pneumonic
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Reactivity series of metal actual
K - Potassium
Na - Sodium
Ca - Calcium
Mg - Magnesium
Al - Aluminium
Zn - Zinc
Fe - Iron
Sn - Tin
Pb - Lead
[H] - hydrogen
Cu - Copper
Hg - Mercury
Ag - Silver
Au - Gold
Pt - Platinium
What is electrolysis
On passing electric current in a molten or aqueous solution a chemical reaction takes place in an ionic compound an it disassociates into its elements.
Electrodes
Electrical conductors (metals) which allow for the flow of charge to pass
Active Electrodes
Interfere with electrolysis reaction. They are mainly metals with low reactivity
Inert electrodes
Dont interfere in electrolysis reaction. Mainly graphite of platinum
Electrolytic cell
Any appartus used in electrolysis
Electrolyte
Ionic compound in liquid/molten/aqueous state
Cathode
Negatively charged electrode (always connected to negative terminal of battery)
Attracts cations in compound
Reduction takes place at cathode due to gain of electrons
Anode
Positively charged cathode (always connected to positive terminal of battery)
Attract anions in compound
Oxidation takes place due to loss of electrons
When current flows in electrolyte vs when current flows in electrode +wires who carry the charge
Electrolyte =Ions
Electrode + Wires = electrons
Does cathode attract more reactive or less reactive metals
Less reactive
Anode formula for electrolysis for OH^-1
4OH^-1 = O_2 + 2H_2O + 4e^-1
Which ions and elements move to cathode
Hydrogen and Metal Ions
Factors affecting deposition in Electrolysis using Active electrode
Time
Voltage/Potential Difference
Concentration
What all changes can be seen when an inert electrode is used
Colour of electrolyte fades as ions are leaving the solution
No change in mass of Anode
Cathode mass increase as a layer of solid is being deposited on the cathode.
What all changes can be seen when an active electrode is used
colour of electrolyte remains the same as ions keep flowing back in the solution
Anode mass decreases
Cathode mass increase
How does increasing the concentration affect the rate of deposition
Increasing the concentration means more ions are present in the electrolyte and hence a greater number of ions will be attracted to the cathode forming a greater deposition layer
How does increasing the potential difference affect the rate of deposition
Higher voltage leads to more movement of ions in the electrolyte, resulting in a greater number of metal ions being deposited on the cathode. According to Ohm’s Law, a greater voltage supplied means a greater current flowing through the electrolyte. Increased current enhances the rate at which metal ions are reduced and deposited on the cathode, with more ions moving towards the cathode per unit time
How does increasing the time affect the rate of deposition
Increasing the time means a longer duration for the ions to deposit onto the cathode, hence a greater rate of deposition
What interference will the active electrodes have on electrolysis
At Anode, the deposition of anions will happen, however, the electrons present in element of anode will also be pulled by the battery and hence the the newly formed ions from the anode will deposit into the electrolyte, refilling the hole leaved by the cation present in the electrolyte being attached to the cathode
Electroplating material of anode and electrolyte
Must be the material or contain the material you wish to electroplate on cathode. Metal in electrolyte must be same as Anode
The object you want to electroplate must be the
Cathode
Salt Bridge
Helps maintain neutrality of solution and helps in movement of ions (cations move to cathode and anion move to anode)
Use metal of high reactivity to ensure no interference in reaction
Factors affecting Voltage in Voltaic Cell
Electrode Material - Different materials have different tendencies to lose or gain electrons
Electrolyte concentration - Increasing the electrolyte concentration in a voltaic cell increases the voltage by enhancing the availability of ions for the reaction
Surface Area of electrode - A larger surface area allows for more contact between the electrode and electrolyte hence a greater voltage
Temperature - Higher temperature means a higher resistance making it harder for current to flow
