General revision Flashcards
What gives a violet colour if shaken with organic solvent
Iodine
What are the conditions when chlorine reacts with sodium hydroxide to form bleach
Cold and dilute
The reactivity of group 2 elements increases down the group, explain why (3 marks)
Increasing size:
Atomic radius increases
OR
more shells
OR
more (electron) shielding
Attraction
Nuclear attraction decreases
OR
(outer) electron(s) experience less attraction
Ionisation energy
Ionisation energy decreases
OR
less energy needed to remove electron(s)
State 2 sources of nitrogen oxides in the stratosphere
- Lightning/ thunderstorms
- Aircrafts
What type of reaction has the greatest atom economy
- Substitution
- Hydrolysis
- Elimination
- Addition
Addition
Define stereoisomer
Same structural formula and different arrangement of atoms in space
Suggest whether the enthalpy change of vapourisation of bromine is exothermic or endothermic. Explain your answer
Endothermic, Energy required to overcome induced dipole–dipole
forces/London forces
Explain in terms of bonds breaking and bond forming, why a reaction can be exothermic
More energy is released by forming bonds
than energy required when breaking bonds
Define the standard enthalpy change of combustion (3 marks)
-(enthalpy change that occurs) when one mole of a
substance
- completely combusts OR reacts fully with oxygen
- 298 K / 25 °C AND 1 atm / 100 kPa / 101 kPa / 105 Pa
/ 1 bar
What is meant by the term average bond enthalpy (2 marks)
(Average enthalpy change) when one mole of bonds
✓
of (gaseous covalent) bonds is broken
Explain the term stereoisomerism
Same molecular formula
AND
Different structural formulae
What are the conditions when a carboxylic acid reacts with an alcohol to form an ester
Heat under reflux
Describe in terms of orbital overlap the similarities and differences between the bonding in Kekule model and the delocalised model of benzene (3 marks)
Similarities
- Orbital overlap
(sideways) overlap of p orbitals
- π bond
π bond/system/ring above and below (bonding (C)
atoms/ring/plane)
Difference
Kekule has: alternating π bonds OR 3 π bonds /
localised (π electrons) / overlap in one direction /
2 electrons in π bond
AND
Delocalised has: π ring (system) / all p orbitals
overlap OR (π electrons) spread around ring / overlap
in both directions / 6 electrons in π bond /
Describe 2 pieces of evidence to support the delocalised model of benzene (2 marks)
Bond length
(C–C) bond length is between single (C–C) and
double bond (C=C)
OR all (C–C) bond lengths are the same
ΔH hydrogenation
∆H hydrogenation less (exothermic) than
expected
Resistance to reaction
Benzene is less reactive than alkenes
OR bromination of benzene requires a
catalyst/halogen carrier
OR benzene does not react with/decolourise
bromine (at room temperature)
OR benzene reacts by substitution
OR benzene does not (readily) react by addition
What is meant by heterolytic fission
Heterolytic
one (bonded) atom/O receives both/2 electrons
Fission
Breaking of a covalent bond
OR breaking of C-O bond
Define relative isotopic mass
The mass of an atom of the isotope compared with 1/12th the mass of an atom of carbon-12
Define relative atomic mass of an element
The weighted mean mass of an atom of an element compared with 1/12th the mass of an atom of carbon-12
Define relative molecular mass of a substance
The weighted mean mass of a molecule of that substance compared to 1/12th of the mass of an atom of carbon-12
Define relative formula mass of a substance
The average mass of a formula unit of that substance compared to 1/12th of the mass of an atom of carbon-12
Give chemical explanations for the following statements. The carbon–carbon bonds in benzene are all the same length
π bonds in benzene are delocalised
The graph shows that rate of reaction decreases over time, explain why in terms of collision theory (2)
- Reactant concentration decreases
- So there’s less frequent successful collisions
Explain how a catalyst increases the rate of reaction (2)
- Catalyst lowers activation energy
- Greater proportion of molecules have energy greater than the activation energy
Describe and explain the effect of increasing the pressure on the rate of reaction(2)
(Increase in pressure) increases the rate
and because molecules are closer together… (1)
… so there are more collisions per unit time (1)
Explain why use if catalyst reduces energy demands and benefits the environment (2)
Lower temperatures / less heat / less thermal energy
* Less fossil fuels / oil / coal / gas / non-renewable fuels
* Reduces CO2 emissions
Explain why use of catakystcan reduce the demand for energy
Allows reactions to take place at lower temperatures
Explain how a concentration/ time graph shows zero order (1 mark)
- Constant gradient
- Linear negative gradient
- Constant rate
- Rate independent of concentration
- Decreasing half life
Explain how an initial rate/ concentration graph shows first order (1 mark)
- Straight line through (0,0)
- Rate directly proportional to concentration
- When the concentration doubles the rate doubles
How do you calculate the value of the pre-exponential factor A using a graph
The y-intercept is equal to lnA
Other than measuring volume of gas produced how else could the rate of reaction be followed
Measure mass loss
How do you calculate the initial rate when given concentration/ time graph
- Draw a tangent on graph at t=0
- Determine the gradient
- Then remember to give units
How do you determine the order of a molecule when given a concentration/ time graph (2 methods)
- Determine half lives, 2 constant half lives indicate first order
- Find 2 gradients = 2 rates, then sub into the Rate=k[x] equation
What is the equation to find k when you know the half lives
k = ln2/ half life
Explain how you could determine the activation energy for the reaction graphically using values of k and T (3 marks)
- Plot graph using lnk and 1/T
- Measure gradient
- Activation energy = -R x gradient
What is meant by the rate determining step
The slowest/ slow step
