Energy And Electrochemistry Flashcards
Energy which is stored within every atom, molecule or ion is a sum of the what and what
Potential (stored) and kinetic energy
The total energy stored in a substance is called the …?
Enthalpy
The change in enthalpy during a chemical reaction is called what and is denoted by what
Heat of reaction & Δ
What is meant by ΔH^o
Standard enthalpy of reaction is being measured as standard lab conditions have been used
What are the two possible units for enthalpy
kJmol-1 or kJ.g-1
How do we measure enthalpy during a reaction
Heat Produced - Heat of reactants
What’s an exothermic reaction
Chemical reaction which releases heat to the surroundings
In an exothermic reaction should the enthalpy of the products be more or less than the reactants
Less, hence ΔH must be negative
What’s an endothermic reaction
Chemical reactions which absorb heat from the surroundings
What do endothermic reactions cause the temperature of the surroundings to do
Decrease
If a reaction is endothermic must the enthalpy of the products be more or less than that of the reactants
More, hence ΔH will be positive
What is an thermochemical equation
An equation showing the enthalpy change for the reaction
4 things to remember when writing thermochemical equations
Equation must be balanced
State symbols at 25 degrees
Include enthalpy change ΔH
If coefficients are doubled ΔH value must be doubled
Equation for calculating quantity of heat released or absorbed
Heat energy released / absorbed = n(specified substance) x molar enthalpy of reaction
Equation for calculating molar enthalpy change for reaction
ΔH = (mass of water x ΔTtemperature change x Cpwater/ 4.18) / 1000 x number of moles in a substance
Equation involving rearranged ΔH expression
ΔT = (1000 x n x ΔH) / (Cpwater/4.18 x mass of water)
What is a fuel
Substance for producing energy via combustion
Two groups of carbon based fuels
Biomass (biofuels)
Fossil Fuels
What are biofuels
Fuels derived from recently living organisms of their by products
Does burning biofuels result in an increase of carbon dioxide in the earths atmosphere
No as its recently been extracted from atmospheric carbon dioxide by growing plants
What are biofuels in relation to carbon
Carbon neutral
What is a common biofuel
Ethanol is the most widely used biofuel
What are fossil fuels
Fuels formed through the anaerobic breakdown of the remains of plant and tiny marine animals which lived millions of years ago
How is energy obtained from fossil fuels
Obtained through burning them in air
How much of Australia’s energy needs are met by fossil fuels
Around 95%
3 Advantages of using ethanol as an energy source
Renewable,
Emits less harmful air pollutants
Domestically produced
3 benefits of biodiesel
Renewable
Fewer air pollutant emissions overall
Domestically produced
2 disadvantages of ethanol
Slight decrease in fuel economy
Lack of widespread fuel availability
2 disadvantages of biodiesel
Lack of widespread fuel availability
Slightly higher nitric oxide emissions
2 advances of coal
Large reserves
Mined at relatively low cost
2 advantages of crude oil
Easily extracted
Transported easily
3 advantages of natural gas
Easily extracted
Transported easily
Burns more cleanly than other fossil fuels
What are the two main disadvantages of using fossil fuels
They’re a major contributor to the enhanced greenhouse effect
It’s non-renewable
Two disadvantages of coal
Produce oxides of nitrogen (can contribute to acid rain and photochemical smog)
Produce fine soot particles (can cause respiratory problems)
Two disadvantages of crude oil
Produces oxides of nitrogen (can contribute to acid rain and photochemical smog)
Produces fine soot particles (can cause respiratory problems)
How to convert kJ.mol to kJ.g
kJ.mol divided by molar mass
How and what do galvanic cells produce
Electrical energy through spontaneous redox reactions
How and what do electrolytic cells produce
Electrical energy from an external source to cause non spontaneous
Electrons flow from the … Reactive to the … Reactive
Most to Least
In oxidation half equations is the e product or reactant
Product
In reduction half equations is the e a product or reactant
Reactant
AN OIL RIG CAT
Oxidation occurs at the anode
Reduction occurs at the cathode
In relation to anodes what direction do electrons flow
Anode to cathode
The anions in the salt bridge move towards the
Anode
Cations in the salt bridge move towards the
Cathode
Can primary / dry cells be recharged
No
Can secondary cells be recharged
Yes
Electrolytic cells - use … energy from an … Source to cause …
Electrical energy, external sources cause non spontaneous redox reactions
In electrolytic cells what is the charge of the anode and cathode
Anode - positive
Cathode - negative
What is the reaction at the anode is water is more reactive
2H2O -> O2 + 4H^+ + 4ē
What is the reaction at the cathode if water is more reactive
H2O + 2ē -> 2OH^- + H2
Overall reaction if water is more reactive at the anode and cathode
6H2O -> 2H2 + O2 + 4H+ + 4OH^-
At the cathode molten metals will be ‘…’
Reduced
At the cathode metals in aqueous solution more reactive than what will be what
Aluminium, reduced
In aqueous solutions what is most likely to be reduced
Very reactive metals and water
At the anode liquids and anions will be what
Oxidised
In aqueous solutions an active metal anode will be oxidised in preference to what
Water
Electrical efficiency of a fuel cell
70-80%
Theoretically how long can fuel cells produce energy for
For as long as the fuel and oxidant are supplied to the electrodes
