Developing Fuels Flashcards
What is the ideal gas equation?
pV=nRT
Pressure x volume = moles x 8.314 x temp K
Pa x m^3 = moles x J/K/mol x K
What volume of gas does 1 mole of a substance take up?
24dm^3 at room temp and pressure
How do you convert cm^3 to dm^3
divide by 1000
How do you convert dm^3 to m^3
divide by 1000
In the ideal gas equation what is volume measured in?
m^3
In the ideal gas equation what is temperature measured in?
Kelvin
How do you convert Celsius to Kelvin
Add 273
What can you use to measure gas produced by a reaction?
A gas syringe
In chemistry what is room temperature and pressure?
298 K (25 Celcius) 100KPa
Whats the equation for volume of gas at RTP
Moles = (volume in dm^3) / 24
What causes a change in enthalpy in a reaction?
bonds being made and broken
What are the standard conditions
298K and 100KPa
What are the four main stages of heterogeneous catalysis
Stage 1: adsorption to catalyst
Stage 2: reactants bonds break
Stage 3: New bonds made
Stage 4: Loss of product from catalyst surface
When calculating enthalpy changes do you pay attention to moles in the reaction
Yes - times by average bond enthalpy
What is standard enthalpy change of reaction?
Enthalpy change when reaction occurs in the molar quantities shown in chemical reaction
under standard conditions
What is the standard enthalpy change of formation?
enthalpy change when 1 mole of a compound is formed from its elements in standard states under standard conditions
What is standard enthalpy change of combustion
enthalpy change when 1 mole of a substance is completely burnt in oxygen under standard conditions
How do you calculate enthalpy change of reaction
(Energy absorbed to break bonds) - (Total energy released in making bonds)
Using average bond enthalpies
What states must compounds be in when bond enthalpies are measured?
gas
What do you do to work out number of molecules?
work out moles and times by avogadro’s constant
What is an exothermic reaction?
A reaction which gives out energy
What does a shorter bond length mean?
Means a stronger attraction and higher bond enthalpy
What is average bond enthalpy?
the energy need to break one mole of bonds in the gas phase
averaged over many different compounds (explains why it’s not exact)
What is bond length?
Distance between two positive nuclei repelling and the attraction of electrons balanced
What are bond enthalpies measured in?
KJ/mol
Is bond breaking exothermic or endothermic?
endothermic
Is bond making exothermic or endothermic
exothermic
What is an endothermic reaction?
absorbs energy - temp decreases
What is Hess’s law?
The total enthalpy change of a reaction is always the same no matter what route is taken
Do moles matter when calculating enthalpy changes using Hess’s cycles and standard enthalpies?
Yes (times amount of moles of product by enthalpy change for it)
What does an enthalpy level diagram look like for an endothermic reaction?
products higher than reactants
what does an enthalpy level diagram look like for an exothermic reaction?
reactants higher than products
What’s different about an enthalpy level diagram with a catalyst?
It has two bumps
What is activation energy?
minimum amount of energy needed to begin breaking bonds and start a chemical reaction
What does less enthalpy mean for a substance?
more stable
What is the equation for enthalpy changes?
q = mcΔT q= heat change m= mass of water or solution
What is standard enthalpy change of neutralisation?
Enthalpy change when an acid and alkali react to form 1 mole of water
Why is the enthalpy of combustion in a lab likely to be a lower value then in a data book?
not done in standard conditions
In q=mcΔT does it matter if T is kelvin or celsius?
no
What is a catalyst?
Increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy
The catalyst is chemically unchanged at the end of the reaction
What catalyst is used in the haber process?
iron
Fe
N2 + 3H2 –> 2NH3
What is used to test for alkene products?
bromine water
why are catalysts used in cracking?
without one it requires high temp and pressure making it expensive
How are catalysts used in cracking
Hydrocarbon vapour over heated solid catalyst
