AS Chemistry Salters F332 4-7 mark question cards

Please let me know in the comments what I can do to make this better

Having read many a mark scheme I have seen the general pattern of the long 4-7 mark answers so here are some cards showing a good way to answer them using the desired vocabulary

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  • Created by: Jamal
  • Created on: 25-05-13 18:52

How do Instantaneous - Induced Dipoles arise.

1. Electron movement within the molecule causes an uneven distribution of charge.

2. This causes an instantaneous dipole in the molecule where one atom has a partial (+ or -) charge.

3. This then induces a dipole in neighbouring molecules  which are attracted to the instantaneously dipoled molecule

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Temperature effect on reaction rate

Description:

1. rate increases on temperature increase*

Explanation:

2. reactant molecules have more kinetic energy

3. this allows a greater likelihood of successful collisions of reactants per unit of time

4. due to more reactants colliding with an energy of at least the activation enthalpy

*Must give clear indication that there is a link between the Increase of temperaure on rate

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Pressure effect on reaction rate

1. Increase in pressure increases the rate of reaction

2. There are more particles in the reaction vessel per unit of volume

3. Greater frequency of collision of reactant particles

Increased pressure shifts the position of equilibrium to the side with the fewest number of molecules

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What is ultraviolet dissociation

1. High (energy or frequency) ultraviolet radiation

2. Causes photodissociation 

3. Bonds in the molecule break

4. Form radicals

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How does CO2 concentration affect global warming

1. The sun emits UV radiation

2. The earth absorbs sun's radiation and (re-emits/radiates) i.r. radiation 

3. CO2 molecules in troposphere absorb i.r. radiation causing the CO2 bonds to gain energy and vibrate

4. The CO2 molecules release the kinetic energy from vibration as thermal energy thus increasing the temperature of the earth (because less heat energy escapes/heat energy is trapped)

5. Some CO2 molecules radiate i.r. radiation

6. The more CO2 molecules in the trophosphere means more heat released to the earth's surface thus causing Global Warming

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How do CFCs contribute to Ozone depletion

1. CFCs are not broken down in the Troposphere because they are too unreactive

2. CFCs are broken down by the sun's high energy UV radiation in the stratosphere via photodissociation

3. This releases Chlorine radicals

4. Chlorine radicals are highly reactive and (react with/break down) ozone to form O2 and O

5. Chlorine radical act as catalysts because they can be re-used to break down more ozone

Iodine radicals are reactive and tend not to reach the stratosphere

Fluorine has a lower ozone depletion potential than Chlorine because Fluorine radicals tend to react with H2O and methane in the stratosphere to form HF which has a strong covalent bond which is not broken down easily by photodissociation

Bromine has a lower ozone depletion potential than Chlorine (but Bromine is more efficient than Chlorine at ozone depletion) because there is less Bromine in the stratosphere because the bond in a bromoalkane (C-Br) is weaker than the bond in a Chloroalkane (C-Cl), therefore bromoalkanes tend to get broken down in the troposphere

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Why are Alcohols liquid but Alkanes gas at 298K

1. Alcohols have an O-H group which allows the formation of hydrogen bonds between molecules

2. Alkanes can only form Instantaneous dipole - Induced dipole forces between molecules

3. Hydrogen bonds are stronger than Instantaneous dipole - Induced dipole forces

4. More energy is required to break the intermolecular forces between alcohols than those of alkanes. Therefore alcohols have a higher (melting/boiling) point

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Why is Iodine solid but Chlorine gaseous at 298K

1.  Electron movement within the molecule causes an uneven distribution of charge.

2. This causes an instantaneous dipole in the molecule where one atom has a partial (+ or -)charge.

3. This then induces a dipole in neighbouring molecules  which are attracted to the instantaneously dipoled molecule

4. Bromine has more electrons in its molecule than Chlorine

5. Therefore stronger dipole

6. Therefore more energy is needed to break the interomlecular forces between Bromine molecules

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How do Hydrogen bonds arise

1. When Hydrogen is bonded to a highly electronegative atom (i.e. Fluorine, Oxygen and Nitrogen) there is a great difference in electronegativity

2. This difference in electronegativity polarises the Hydrogen atom making it partially positive

3. The partially positive Hydrogen atom is then attracted to the lone pair of neighbouring Fluorine or Nitrogen or Oxygen atoms that are bonded to Hydrogen atoms

Sometimes it helps to draw the bond taking place. Don't forget the partial charges.

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