1.
State what is meant by lattice enthalpy.
[1 mark]
- formation of a solid lattice from gaseous ions
JD SCIENCE
Physical chemistry 3 — thermodynamics, rates and electrochemistry
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by Gibbs free energy.
[1 mark]
- ΔG = ΔH − TΔS
3.
State what is meant by the Arrhenius equation.
[1 mark]
- k = Ae^{−Ea/RT}
4.
State what is meant by a half-cell.
[1 mark]
- metal in a solution of its ions
5.
State what is meant by EMF of a cell.
[1 mark]
- Eθred − Eθox / more positive minus more negative
6.
State what is meant by a buffer.
[1 mark]
- resists pH change
7.
State what is meant by pH of a strong acid.
[1 mark]
- pH = −log[H⁺]
8.
State what is meant by Ka.
[1 mark]
- acid dissociation constant
9.
State what is meant by a redox titration.
[1 mark]
- e.g. manganate(VII) with Fe²⁺
10.
State what is meant by electrochemical series.
[1 mark]
- order of Eθ values
11.
Amira is asked about lattice enthalpy in a AQA Chemistry paper.
(a) [2 marks]
- more exothermic if ions small/high charge
(b) [3 marks]
- Born–Haber
12.
Amira is asked about Gibbs free energy in a AQA Chemistry paper.
(a) [2 marks]
- feasible if ΔG < 0
(b) [3 marks]
- T can change feasibility
13.
Amira is asked about the Arrhenius equation in a AQA Chemistry paper.
(a) [2 marks]
- ln k vs 1/T is a straight line
(b) [3 marks]
- gradient −Ea/R
14.
Amira is asked about a half-cell in a AQA Chemistry paper.
(a) [2 marks]
- Eθ vs SHE
(b) [3 marks]
- more positive, easier reduction
15.
Amira is asked about EMF of a cell in a AQA Chemistry paper.
(a) [2 marks]
- spontaneous if Ecell > 0
(b) [3 marks]
- standard conditions
16.
Amira is asked about a buffer in a AQA Chemistry paper.
(a) [2 marks]
- weak acid + salt
(b) [3 marks]
- HA ⇌ H⁺ + A⁻
17.
pH of 0.020 mol dm⁻³ HCl
[3 marks]
- Final answer: 1.70
18.
[H⁺] if pH=3.00
[3 marks]
- Final answer: 1.0 × 10⁻³ mol dm⁻³
19.
ΔG if ΔH=−20 kJ, ΔS=−50 J K⁻¹, T=300 K
[3 marks]
- Final answer: −5 kJ
20.
Ecell if 0.80 − (−0.76)
[3 marks]
- Final answer: 1.56 V
21.
Ka = 1.8×10⁻⁵, [HA]=0.10. [H⁺] ≈
[3 marks]
- Final answer: 1.3 × 10⁻³
22.
Titration: 25.0 cm³ Fe²⁺ needs 20.0 cm³ of 0.0200 mol dm⁻³ MnO₄⁻. Moles MnO₄⁻
[3 marks]
- Final answer: 4.00 × 10⁻⁴
23.
Amira carries out a AQA-style required practical linked to thermodynamics, rates, electrode potentials and acids. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: the independent variable for this topic
- Dependent: the measured outcome
(b) [2 marks]
- keep all other variables constant
- so the test is fair / only one variable is changed
(c) [2 marks]
- repeat and calculate a mean / use a tighter method
24.
Amira carries out collecting valid data for thermodynamics, rates, electrode potentials and acids. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: a chosen factor
- Dependent: a quantitative measurement
(b) [2 marks]
- calibrated instrument
- so the test is fair / only one variable is changed
(c) [2 marks]
- systematic error from zero error
25.
Amira carries out drawing a graph for thermodynamics, rates, electrode potentials and acids. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: x-variable
- Dependent: y-variable
(b) [2 marks]
- same scale / same apparatus
- so the test is fair / only one variable is changed
(c) [2 marks]
- not drawing a line of best fit through the trend
26.
Amira carries out evaluating a method about thermodynamics, rates, electrode potentials and acids. This is a typical AQA required-practical style question.
(a) [2 marks]
- Independent: method change
- Dependent: precision / accuracy
(b) [2 marks]
- same sample size
- so the test is fair / only one variable is changed
(c) [2 marks]
- too few repeats
27.
Compare lattice enthalpy with Gibbs free energy.
[4 marks]
- formation of a solid lattice from gaseous ions
- ΔG = ΔH − TΔS
- give one linked difference
28.
Compare Gibbs free energy with the Arrhenius equation.
[4 marks]
- ΔG = ΔH − TΔS
- k = Ae^{−Ea/RT}
- give one linked difference
29.
Compare the Arrhenius equation with a half-cell.
[4 marks]
- k = Ae^{−Ea/RT}
- metal in a solution of its ions
- give one linked difference
30.
Compare a half-cell with EMF of a cell.
[4 marks]
- metal in a solution of its ions
- Eθred − Eθox / more positive minus more negative
- give one linked difference
31.
Apply your knowledge of pH of a strong acid to this situation: [H⁺]=concentration if monoprotic
[3 marks]
- [H⁺]=concentration if monoprotic
32.
Apply your knowledge of Ka to this situation: pKa = −log Ka
[3 marks]
- pKa = −log Ka