What is the standard state?
The physical state of substances under standard conditions
- 298 K
- 101 KPa
- 1 mol dm-3
What is the enthalpy change of combustion?
The enthalpy change when 1 mole of a substance burns completely in oxygen under standard conditions.
What is the equation for the change in energy?
Change in energy (J) = mass of water (g) x specific heat capacity (Jg-1K-1) x change in temperature (K)
What is the specific heat capacity of water?
4.18 Jg-1 K-1
What is the enthalpy change of reaction?
The enthalpy change that occurs when molar quantities of reactants stated in the equations react together under standard conditions.
Reactants and products are in standard states
What is the equation for energy density?
Energy (J)
Energy density (Jg-1) = ——————————
Mass of fuel used (g)
What happens during an endothermic reaction?
Overall bonds are breaking which requires energy.
ΔH is positive
What happens during an exothermic reaction?
Overall bonds are made which releases energy.
So ΔH is negative
What is the average bond enthalpy?
The mean amount of energy required to break 1 mole of a particular bond in a gaseous molecule
How is enthalpy change calculated?
Sum of bonds broken - sum of bonds made
How is bond enthalpy linked to the length of the bond?
The shorter the bond, the higher the bond enthalpy
A greater electron density means a stronger force of attraction therefore a shorter bond length
What is the enthalpy change of neutralisation?
The enthalpy change that occurs when 1 mole of H+ reacts with 1 mole of H2O under standard conditions in solutions with a concentration of 1 mol dm-3
Enthalpy change of neutralisation is always the same
What is Hess’s law and why is it useful?
The total enthalpy change of a reaction is independent of the route taken provided that the initial and final conditions of the reaction stay the same
It means enthalpy change can be calculated indirectly
Why may enthalpy change be unable to be measured?
- Slow rate
- High activation energy
- More than 1 reaction takes place
What are the steps for naming an organic molecule?
1- Find the longest carbon chain
2- Find the name of the side chain (e.g. methyl/ethyl)
3- Find the position of the side chain (Lowest possible no. combination)
4- Combine the names
What are the 3 types of structural isomers and what is structural isomerism?
- Atoms are bonded in a different order
Chain isomers - different length and position of side chains
Position isomers - functional groups on different carbons
Functional group isomers - where the molecules have different functional groups
What is a stereoisomer and what are the 2 forms of stereoisomers?
- Molecules with the same structural formula, but a different arrangement of atoms in space
Optical isomer - The attachment of 4 different functional groups around a carbon atom
Geometric isomer - E/Z or cis/trans isomers
- molecule has a C=C double bond and different atoms or groups attached to the C=C
What is a cis-isomer?
Cis-isomers have the lightest groups on the same side of the C=C double bond (horizontally in bow tie)
If the lightest groups are both hydrogen, prefix Z is also applicable
What is a trans-isomer?
Trans-isomers have the lightest groups on opposite sides of the C=C double bond (diagonally in bow tie)
If both of the lightest groups are hydrogen, prefix E is applicable
What is cracking and how is it done?
- Taking hydrocarbon chains and breaking them down into smaller, more useful ones
Done with: - An aluminium catalyst at high temperature
- Steam at high pressure
What happens to bromine water when alkenes are added?
Turns from orange to colourless as bromine reacts with the double bond in the alkene
What is electronegativity?
- A measure of the attraction of the atoms in a covalent bond for the electrons in the bond
- increases up and to the right of a group
What is electrophilic addition?
An Alkene and an elctrophile form a carbocation and negative ion the the product
What is an electrophile?
A electron pair acceptor
