Energy and Energy Changes
What name is given to a reaction that absorbs heat from its surroundings?
Endothermic reaction
In a redox reaction, oxidation involves the (gain/loss) of electrons.
Loss of electrons.
What is the name of the point where the indicator changes color in titration?
Endpoint.
Define a lewis acid
A lewis acid is an electron paid acceptor
What color precipitate does silver nitrate form with chloride ions?
White precipitate (AgCl).
State whether the following process is exothermic or endothermic: Ice melting at room temperature.
Endothermic.
Identify the oxidizing agent in the reaction:
Zn + Cu²⁺ → Zn²⁺ + Cu
Cu²⁺ (because it gains electrons).
What apparatus is used to accurately measure the volume of a solution delivered during a titration?
Burette
What is the pH of 0.001 M NaOH solution at 25oC?
11
What term describes the minimum energy needed for a chemical reaction to occur?
Activation energy
Calculate the heat absorbed when 250 g of water is heated from 20 °C to 50 °C.
(Specific heat capacity of water = 4.18 J/g°C)
31,350 J (≈ 31.35 kJ)
Explain why oxidation and reduction reactions are complementary
Every electron lost must be gained. Hence they occur simultaneously
If 25.0 mL of NaOH neutralizes 20.0 mL of 0.10 M HCl, calculate the molarity of the NaOH.
HCl + NaOH → NaCl + H₂O
moles HCl = 0.10 × 0.020 = 0.002 mol
Molarity NaOH = moles / volume = 0.002 / 0.025
Answer: 0.080 M NaOH
H3O+ reacts with all the following except
A. NaOH
B. Na2SO4
C. KHCO3
D. MgCO3
B. Na2SO4
Which of the following processes is not a chemical change?
A. Polymerisation
B. Crystallization
C. Electrolysis
D. Corrosion
B. Crystallization
Write an equation to represent the following: The standard enthalphy of combustion of ethanol is -1420 kJ/mol
C2H5OH + 3O2 - 2CO2 + 3H2O
H = -1420 kJ/mol
In which of the following compounds is the oxidation number of sulphur +4?
A. H2SO4
B. SO3
C. H2SO3
D. Na2S2O3
C. H2SO3
35.0 mL of 0.200 M H₂SO₄ is used to neutralize NaOH.
Find the moles of NaOH required.
Reaction: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
moles H₂SO₄ = 0.200 × 0.035 = 0.007 mol
moles NaOH = 2 × 0.007 = 0.014 mol
Solid iron (III) chloride turns liquid on exposure to air because it is
deliquescent
What is water of crystallization?
Water of crystallization is defined as a fixed amount of water molecules which accompanies a crystal when the substance is obtained from aqueous solution.
Use the bond dissociation energies to calculate the enthalphy of the reaction:
C-C = 347,
C=C - 610
H-Cl - 341
C-Cl - 339
C-H - 414
-149 kK/mol
How many electrons are transferred when dichromate ion (Cr₂O₇²⁻) is reduced to Cr³⁺ in acidic solution?
Each Cr⁶⁺ → Cr³⁺ = 3 electrons
Two Cr atoms → 6 electrons total.
A student titrates 25.0 mL of monoprotic acid with 0.150 M NaOH and uses 18.40 mL to reach equivalence.
Calculate the acid concentration.
moles NaOH = 0.150 × 0.0184 = 0.00276 mol
Monoprotic → moles acid = moles base
Concentration acid = 0.00276 / 0.025 = 0.1104 M
The pka for propanoic acid is 4.9. Calculate the pH of a 0.01M solution of the acid
3.5
What pH value is considered neutral
pH 7