R1: Flashcards
What is standard enthalpy of formation?
Enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions
What is standard enthalpy of atomisation?
Enthalpy change when one mole of gaseous atoms are formed under standard conditions
What is standard enthalpy of combustion?
Enthalpy change when one mole of a substance completely reacts with oxygen to form its products under standard conditions
Heat vs temperature
Heat - measure of total energy of a substance - so depends on amount of substance present
Temperature - measure of average kinetic energy of particles in a substance
Describe the enthalpy change, temperature changes and flow of heat in exothermic reactions
Heat flows from system to surroundings. Temperature of surroundings increases.
Enthalpy change is negative
Describe the enthalpy change, temperature changes and flow of heat in endothermic reactions
Heat flows from surroundings to system.
Temperature of surroundings decreases.
Enthalpy change is positive.
% Error equation
(Experimental value - Literature value / literature value) x 100
What is average bond enthalpy?
energy required to break one mole of bonds in a gaseous molecule averaged over different molecules
How does enthalpy of combustion change as carbon chain length increases in alkanes and alcohols?
Increases
What is coal and how is it formed?
Solid fossil fuel made primarily of carbon. Formed from fossilisation of vegetation due to pressure and heat.
What is natural gas and how is it formed?
Gaseous fossil fuel made primarily of methane with other hydrocarbons. Formed from fossilisation of marine microorganisms due to heat and pressure.
What is crude oil and how is it formed?
Liquid fossil fuel made of a mixture of hydrocarbons. Formed from fossilisation of marine microorganisms due to heat and pressure.
Pros and cons of fossil fuels
Pros - cheap, high energy density, high abundance
Cons - CO is toxic, CO2 is a greenhouse gas (natural gas ONLY produces CO2), SO2 creates acid rain, non-renewable, Natural gas and crude oil can have leaks
Which fossil fuels emits the least CO2 per unit of energy released?
Natural gas
What is biofuel?
Fuel derived from biological carbon fixation in biomass
What is the process of producing biofuel?
Fermenting starchy plants which forms ethanol from glucose, then mixing that with gasoline.
Pros and cons of biofuels
Pros - renewable, release lower net emissions
Cons - less land for food production, lower specific energy than fossil fuels
What are fuel cells?
Fuel cells which transfers chemical energy to electrical energy from the redox reaction between hydrogen/methanol and oxygen to form water.
Half equations in a hydrogen fuel cell
At anode:
2H2 –> 4H+ + 4e-
At cathode:
O2 + 4e- + 4H+ –> 2H2O
Half equations in a methanol fuel cell
At anode:
2CH3OH + 2H2O –> 2CO2 + 12H+ + 12e-
At cathode:
12H+ + 12e- + 3O2 –> 6H2O
What is entropy (S)?
The measure of the ways in which available energy in a system can be distributed among particles. Also a measure of disorder.
Do natural systems tend towards an increase or decrease in entropy?
Increase
Order these in terms of entropy: Liquid, Solid, Gas
Highest entropy
Gas
Liquid
Solid
Lowest entropy
Which types of chemical reaction would have positive entropy?
1) Dissolving a solid in a liquid to form a solution
2) Changing state by heating (s to l, s to g, l to g)
3) Making more moles of a substance
Does positive or negative entropy represent a spontaneous reaction?
Positive
What is the equation for finding entropy change?
Sum of entropy of products - Sum of entropy of reactants
What is Gibbs free energy?
Measure of the energy obtained from a reaction which is able to do work. Also a measure of spontinaety
For a non-spontaneous process, is change in Gibbs energy positive or negative?
Positive
Under what conditions can entropy be equal to 0?
Perfect crystal, pure substance, temp=0K
