Chemical Equilibrium
What term describes the state in a reversible reaction where the forward and reverse rates are equal, keeping concentrations constant?
Dynamic equilibrium
In Brønsted-Lowry theory, what is the substance that donates a proton (H+)?
Acid
What is the goal of completing a titration?
To determine the concentration of an unknown solution (analyte/titrand) by reacting it with a solution of known concentration (titrant).
What happens to a substance when it is oxidised?
It loses electrons (OIL RIG)
What is a galvanic cell?
A cell that converts chemical energy into electrical energy via a spontaneous redox reaction.
What is the name of a system where energy but not matter can be exchanged with the surroundings?
Closed system
What is the pH of pure water at 25°C, where [H+]=[OH-]=1x10^-7 mol/L?
pH = 7
What is the equivalence point in a titration?
The point where the added titrant (known concentration) has completely neutralised the titrand (unknown concentration).
What is the oxidation number of any element in their elemental state, e.g. O2, Cu(s)?
0
What is the negatively-charged electrode in a galvanic cell?
The anode, this is where oxidation occurs.
Oxidation is loss, electrons flow from negative to positive.
Which principle predicts a system at equilibrium will shift to partially counteract any imposed change?
Le Chatelier's principle
What is a molecule that partially dissociates in water called?
Weak acid
What is an indicator?
A weak acid or base that changes colour symbolising the endpoint of a reaction (colour change).
A species that donates electrons, causing another species to be reduced (RIG).
What is the point of having a salt bridge in a galvanic cell?
The component that links the two half-cells, allowing ion flow to maintain neutrality without mixing solutions.
For the exothermic reaction 2SO2(g)+O2(g)⇌2SO3(g), what is the direction of equilibrium shift when temperature increases?
Left (towards reactants)
What is the pH of a 0.01 mol/L solution of the strong acid HNO3?
2
Because pH = -log(H+)
What is the concentration of HCl when 20 mL of 0.1 mol/L NaOH exactly neutralises 40 mL of HCl?
0.05mol/L
Because C1V1 = C2V2
What is the oxidation number of S in the sulfate ion, SO4^2-?
+6
What is the E° of a cell with a copper cathode and zinc anode?
What is the equilibrium consant for H2+I2⇌2HI: [H2]=0.5M, [I2]=0.5M, [HI]=2M?
16
What is the pH of a solution with [OH-]=1x10^-5 mol/L at 25°C (Kw=1x10^-14)?
9
Because Kw = (H+)(OH-)
Then pH = -log(H+)
What is the concentration of NaOH when 25 mL of 0.2 mol/L H2SO4 neutralises 50 mL NaOH?
(H2SO4+2NaOH→Na2SO4+2H2O)
0.2mol/L
Molar ratio is 2:1
In 2Fe3+ + Sn2+ → 2Fe2+ + Sn4+, what is the total number of electrons transferred?
2 electrons transferred from tin to iron
1. Split into half-equations
2. Balance half-equations
If a galvanic cell is set up: Ag half-cell E°=+0.80V, Fe half-cell E°=-0.44V. Which electrode is the cathode?
Ag is the cathode, because it has a higher reduction potential.