Exam questions Flashcards
Nitric acid
HNO3
Why is there a general increase in ionisation energies across period 2
There is an increases in nuclear charge so the electrons experience a bigger pull from the nucleus. There is little change in atomic radius and shading, so more energy is needed to remove the outermost electron so bigger nuclear attraction
What forms after the first ionisation energy
X+
Electronegativity
The ability of an atom to attract a pair of electrons into a covalent bond
Why do bonds have dipoles
Because there is a big difference in the electronegativity of the elements
How are p orbitals involved in the formation of a C=C double bond
The p orbitals overlap to form a pie bond there are now 2 bonds between the carbons, a pie bond and a sigma bond.
What type of bond fission is involved in the formation of bromine radicals
Homolytic fission
Why do both cis and trans isomers react to form the same product
They no longer have a double bond which restricts movement
What is the role of phosphoric acid in a reaction and why is it added slowly
It acts as a catalyst to speed up the reaction. It is added slowly to prevent high temperatures and side reactions
How is margarine formed
It is manufactured from the hydrogenation of alkenes. The oils are no longer saturated so are solid instead of being liquid. A nickel catalyst is used.
Why are polymers hard to dispose of
They are inert so are not biodegradable. They release toxic fumes when burnt which is bad for the environment.
Low volatility
Does not easily turn into a gas
Intermolecular forces
The forces between the molecules which must be broken in order for the substance to evaporate. They hold the shape of the molecule
Why is ethanal produced in distillation
Because it is distilled to prevent the ethanal from being further oxidised to ethanoic acid. It is heated below the ethanoic acid boiling point so that the ethanal will be collected but not the ethanoic acid.
Why is reflux used to form ethanoic acid
Reflux is used so that any ethanal originally produced will be further oxidised to ethanoic acid
What is also produced when ethanol is oxidised
Water
What would happen if chlorine gas is bubbled through potassium iodide solution followed by cyclohexane
The solution turns brown, then two layers are produced and the top layer is purple
Why can non-polar substances dissolve in non-polar solvents
Because there are only London force in the non-polar substance and solvent. London forces can occur between the non-polar substance and solvent, which weakens the intermolecular forces in the non-polar substance and breaks it up
What happens to the pH of solutions of group 2 hydroxides down the group
The pH increases down the group because they become more soluble down the group so there are more OH- ions in the water.
Bond enthalpy
The energy required to break one mole of a bond in a gaseous state
Suggest two reasons why the standard enthalpy of methanol is different from that calculate
Energy will be lost to the surroundings when calculated experimentally. Incomplete combustion may occur when it is calculated experimentally.
Why can some enthalpy change of reactions not be measured directly
Other products are more likely to be formed and the activation energy may be too high
Units for enthalpy change
KJmol-1
Why does an exothermic reaction occur spontaneously at low temperatures but does not occur at very high temperatures
DeltaS is negative because it goes from 2 moles of gas to one. As the temperature increases the magnitude of TdeltaS increases. At high T, deltaS is more negative then deltaH. DeltaG is positive and the reaction is no longer feasible.
Why would dissolving be exothermic
Because bonds are being broken which is exothermic. Enthalpy of hydration is bigger then lattice enthalpy. Enthalpy of hydration is exothermic and lattice enthalpy is endothermic
What makes a reaction more spontaneous
The lower the value of deltaG is.
How will the experimental lattice enthalpy differ from the calculated one
The experimental lattice enthalpy will be more negative then the theoretical lattice enthalpy, as the theoretical lattice enthalpy only takes into account the ionic bonding and not the covalent characteristics. They will therefore assume that the bond is weaker then it is, so the experimental value will be more negative.
How does electron affinity change as you go down group 7
Down the group the atoms get bigger and are less able to attract an electron due to the increased effect of shielding and atomic radius, this decreases the pull the atom exerts on the electron. Therefore the value for electron affinity becomes less negative down the group.
Define the first ionisation energy (3)
The energy required to remove one electron from each atom in a mole of gaseous atoms
Why is the second ionisation energy greater than the first ionisation energy (1)
There are more protons to electrons so the electrons feel a bigger pull from the nucleus and more energy is required to break this.
What bond will be broken in CF3Cl
The carbon-chlorine bond as it has the lowest bond enthalpy so would require the least energy to break.
Investigating the rate of hydrolyses of chloroethane, bromoethane and iodoethane (5)
You would ass each of the haloalkanes to a test tube, then ethanol and aqueous silver nitrate. You then put it in a water bath set at 50 degrees, and time how long it would take for a precipitate to form. Ag + X- –> AgX(s). X represents a halide. The yellow precipitate from the Iodine will form first, then the cream precipitate from bromine, and finally the white precipitate from the chlorine. Iodine has therefore reacted first because the carbon-iodine bond has the lowest bond enthalpy then the others so less energy is needed to break this bond
Describe and explain the trend in oxidising ability down group 7
The stronger oxidising agents are at the top of the group, as you go down the group atomic radius and shielding increases, this outweighs the increase in nuclear charge. This means that there is less nuclear attraction so it is harder to gain an electron.
How would you test for a carbonate
You add HCl then bubble the gas through lime water, it then turns milky white as a precipitate forms
How do you test for sulfates
Add HCl then BaCl2, a white precipitate will form
