[DF1] What is the ideal gas equation?
pV = nRT
p: pressure (Pa) V: volume (m³) n: number of moles (mol) R: gas constant (8.313 J mol⁻¹ K⁻¹) T: tempreture (K)
[DF1] How can you predict the yield of a reaction?
(e.g. 4Na + O₂ → 2Na₂O)
- Work out the number of moles of a reactant you have used.
(for 2g of Na: 2/23 = 0.087 mol) - Multiply by the ratio between the chosen reactant and product.
(0. 087 x 0.5 = 0.044 mol) - Multiply by the Mᵣ of the product.
(0. 044 x 62 = 2.73g)
[DF2] What is the difference between a π bond and a σ bond?
A σ bond is caused by the direct overlap of the p-orbitals or carbon atoms.
π bonds are caused by the indirect ‘leaning overlap of p-orbitals.
https://drive.google.com/file/d/1SoOShMkBMVTeTVWXH3FekXELkqsEf-dH/view?usp=sharing
[DF2] What is a double bond?
A double bond consists of one π bond and one σ bond.
[DF2] How can you draw a molecule in 3D?
- A solid line represents a bond in the plane of the paper.
- A solid wedge represents a bond coming out of the plane of the paper.
- A dashed/dotted wedge represents a bong going into the plane of the paper.
[DF3] What is the meaning of the term ‘endothermic’?
- Endothermic reactions are those that take energy in from the surroundings:
- The energy needed to break the bond is greater than the energy needed to make the bond in the reaction.
[DF3] What is the meaning of the term ‘exothermic’?
- Exothermic reactions are those that release energy into the surroundings:
- The energy needed to break the bond is less than the energy needed to make the bond in the reaction.
[DF3] What are standard conditions?
- A pressure of 100kPa (1atm)
- A temperature of 298K (room temperature)(25⁰C)
- All solutions are at a concentration of 1 mol dm⁻³ for electrode potentials.
[DF3] Define the standard enthalpy change of reaction, ΔHᵣᶿ.
The enthalpy change that occurs when substances are reacted in the molar ratios as defined by a chemical equation.
The reaction takes place under standard conditions with reactants and products in their standard states.
[DF3] Define the standard enthalpy change of combustion, ΔH꜀ᶿ.
The enthalpy change that occurs when substances are reacted with one mole of oxygen.
The reaction takes place under standard conditions with reactants and products in their standard states.
[DF3] Define the standard enthalpy change of formation, ΔHғᶿ.
The enthalpy change that occurs when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
[DF3] Define the standard enthalpy change of formation, ΔHₙₑᵤₜᶿ.
The enthalpy change that occurs when one mole of water is produced from a neutralisation reaction that happens under standard conditions.
[DF3] What is average bond enthalpy?
The energy needed to break one mole of the standard bond under standard conditions.
[DF3] What relation does bond enthalpy have to bond strength?
The greater the bond enthalpy, the greater the bond strength.
As the bond strength increases the length of the bond decreases.
[DF3] Match the reaction process to the thermal result:
- Bond breaking.
- Bond making.
- Exothermic.
- Endothermic.
- Bond breaking = Endothermic.
- Bond making = Exothermic.
[DF3] What does each term mean in q = mcΔT
q = mcΔT
q: The energy absorbed by the material (normally water) (J)
m: The mass of material being used (g)
c: The specific heat capacity of the material used (c of water = 4.18 Jg⁻¹K⁻¹)
ΔT: The change in temperature of the material (final - initial)
[DF4] What is a catalyst?
- A catalyst is a substance that is not used up in the reaction.
- And helps to increase the rate of reaction by offering a different pathway for the reaction to take.
[DF4] What is catalyst poison?
A substance that reduces the effectiveness of the catalyst by permanently bonding to the active site.
[DF4] What does heterogeneous mean?
- A heterogeneous catalyst is one that does not share the same phase as the reactants.
- For example the solid iron catalyst in the gaseous reaction of hydrogen and nitrogen.
[DF4] What does heterogeneous catalysis look like?
- The reactants form partial bonds with the catalyst, adsorbing onto the surface.
- Because the reactants are in close proximity, successful collisions are more frequent.
[DF4] What is cracking?
The breaking of long-chain alkanes into shorter-chain alkanes and alkenes.
[DF5] What are some common simple molecular pollutants?
- CO.
- CO₂.
- NOₓ.
- SOₓ.
- unburnt hydrocarbons.
[DF5] What are some methods of reducing CO₂ emissions?
Using renewable sources of electricity such as solar or wind power as well as using electric or hydrogen-powered cars can be methods of reducing CO₂ emissions.
[DF5] What are some methods of reducing CO and unburnt hydrocarbons?
Using more efficient engines and catalytic converters in cars.
