Physical Chemistry EXAM QUESTIONS
& ANSWERS 100% CORRECT!
State, in terms of electrons, the meaning of the term oxidising agent. [1] - ANSWER 1. Electron
acceptor
State two features of the current atomic model that are not shown in the Rutherford model. [2] -
ANSWER 1. Nucleus containing protons and neutrons
2. Electrons in energy levels/orbitals
The sample of chronium is analysed in a TOF mass spectrometer. Give two reasons why it is
necessary to ionise the isotopes of chronium before they can be analysed in a TOF mass
spectrometer. [2] - ANSWER 1. Ions charged so will produce current
2. Ions will be accelerated by electric field
The student rinses the burette with deionised water before filling with sodium hydroxide solution.
State and explain the effect that this rinsing will have on the value of the titre. [2] - ANSWER 1. Titre
would increase/larger value
2. Because NaOH would be more dilute
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass
spectometer [2] - ANSWER 1. Ions will interact with and be accelerated by an electric field
2. Only ions will create a current when hitting the detector
Explain qualitatively why doubling the temperature has a much greater effect on rate of the reaction
than doubling the concentration of E. [3] - ANSWER 1. Reaction occurs when molecules have E>Ea
2. Doubling T causes many more molecules to have E>Ea
3. Whereas doubling E only doubles the number with this energy
Rearrange the Arrhenius equation for Ea. [1] - ANSWER 1. Ea= RT (lnA-lnK) /1000
A student completed a series of tests to determine the order of reaction in respect to iodine.
, Suggest why the 1.0cm3 portions of the reaction mixture are added to ab excess of NaHCO3 solution
[2] - ANSWER 1. The sodium hydrogencarbonate solution neutralises the acid catalyst
2. So stops the reaction
Describe how molecules are ionised using electrospray ionisation. [3] - ANSWER 1. Sample dissolved
in volatile solvent
2. Injected through positively charged needle
3. Each molecule/particle gains a proton
The first ionisation energies of the elements in period 2 change as the atomic number increases.
Explain the pattern in the first ionisation energies of the elements from lithium to neon. [6] -
ANSWER 1. Ionisation energy increases a long a period
2. Due to increase in nuclear charge, decrease in atomic radius and same number of electron shells
3. Higher electrostatic attraction between nucleus and outer electron requiring more energy to
overcome
4. Be-B deviation, B lower than Be
5. Outer electron of B in 2p orbital which is higher energy level than 2s
6. N-O deviation, O lower than N
7. Two electrons in 2p orbital need to pair, causing e-e repulsion
Suggest why the order of this reaction with respect to propanone can be ignored in this experiment.
[2] - ANSWER 1. The concentration/amount of propanone is much larger than the amount of iodine
2. Concentration of propanone is almost constant
Explain how a graph shows that the reaction is zero order with respect to iodine in the reaction
between iodine and propanone. [2] - ANSWER 1. The graph has a constant rate
2. So rate does not change as concentration of iodine changes/iodine is used up
For this reaction at 1050K the equilibrium constant, Kp= 7.62x105 Pa
For this reaction at 500K the equilibrium constant, Kp+ 3.94x104 Pa
Explain how this information can be used to deduce that the forward reaction is endothermic. [2] -
ANSWER 1. Kp is higher at higher temps/lower at lower temp
2. At higher temp more dissociation occurs/more products formed/ equilibrium shfits to right
& ANSWERS 100% CORRECT!
State, in terms of electrons, the meaning of the term oxidising agent. [1] - ANSWER 1. Electron
acceptor
State two features of the current atomic model that are not shown in the Rutherford model. [2] -
ANSWER 1. Nucleus containing protons and neutrons
2. Electrons in energy levels/orbitals
The sample of chronium is analysed in a TOF mass spectrometer. Give two reasons why it is
necessary to ionise the isotopes of chronium before they can be analysed in a TOF mass
spectrometer. [2] - ANSWER 1. Ions charged so will produce current
2. Ions will be accelerated by electric field
The student rinses the burette with deionised water before filling with sodium hydroxide solution.
State and explain the effect that this rinsing will have on the value of the titre. [2] - ANSWER 1. Titre
would increase/larger value
2. Because NaOH would be more dilute
Explain why it is necessary to ionise molecules when measuring their mass in a TOF mass
spectometer [2] - ANSWER 1. Ions will interact with and be accelerated by an electric field
2. Only ions will create a current when hitting the detector
Explain qualitatively why doubling the temperature has a much greater effect on rate of the reaction
than doubling the concentration of E. [3] - ANSWER 1. Reaction occurs when molecules have E>Ea
2. Doubling T causes many more molecules to have E>Ea
3. Whereas doubling E only doubles the number with this energy
Rearrange the Arrhenius equation for Ea. [1] - ANSWER 1. Ea= RT (lnA-lnK) /1000
A student completed a series of tests to determine the order of reaction in respect to iodine.
, Suggest why the 1.0cm3 portions of the reaction mixture are added to ab excess of NaHCO3 solution
[2] - ANSWER 1. The sodium hydrogencarbonate solution neutralises the acid catalyst
2. So stops the reaction
Describe how molecules are ionised using electrospray ionisation. [3] - ANSWER 1. Sample dissolved
in volatile solvent
2. Injected through positively charged needle
3. Each molecule/particle gains a proton
The first ionisation energies of the elements in period 2 change as the atomic number increases.
Explain the pattern in the first ionisation energies of the elements from lithium to neon. [6] -
ANSWER 1. Ionisation energy increases a long a period
2. Due to increase in nuclear charge, decrease in atomic radius and same number of electron shells
3. Higher electrostatic attraction between nucleus and outer electron requiring more energy to
overcome
4. Be-B deviation, B lower than Be
5. Outer electron of B in 2p orbital which is higher energy level than 2s
6. N-O deviation, O lower than N
7. Two electrons in 2p orbital need to pair, causing e-e repulsion
Suggest why the order of this reaction with respect to propanone can be ignored in this experiment.
[2] - ANSWER 1. The concentration/amount of propanone is much larger than the amount of iodine
2. Concentration of propanone is almost constant
Explain how a graph shows that the reaction is zero order with respect to iodine in the reaction
between iodine and propanone. [2] - ANSWER 1. The graph has a constant rate
2. So rate does not change as concentration of iodine changes/iodine is used up
For this reaction at 1050K the equilibrium constant, Kp= 7.62x105 Pa
For this reaction at 500K the equilibrium constant, Kp+ 3.94x104 Pa
Explain how this information can be used to deduce that the forward reaction is endothermic. [2] -
ANSWER 1. Kp is higher at higher temps/lower at lower temp
2. At higher temp more dissociation occurs/more products formed/ equilibrium shfits to right
