Chapter Two : Energy calculations Flashcards
Enthalpy definition (heat content)
The total energy stored in a substance (H)
Change in enthalpy (heat of reaction)
Change in heat content when a substance undergoes a chemical reaction and the energy of the reactants is different to the energy of the products
Delta H
Change in heat content equation
Change in heat content = (heat content of products) - (heat content of reactants)
Standard laboratory conditions
25 degrees 1 mole of the substance 1M solutions Heat absorbed or released is in kJ Pressure is 100kPa
Heat of solution definition
Is the change in enthalpy when 1 mole of any substance dissolves in water
Heat of neutralisation definition
Is the change in enthalpy when an acid reacts with a base to form 1 mole of water
Heat of vapourisation definition
Is the change in enthalpy when 1 mole of liquid is converted to gas
Heat of combustion definition
Is the enthalpy change when a substance burns in air, always exothermic
Exothermic reaction facts
When heat is released
Heat content of reactants is greater than products
Bonds in products are stronger than bonds in reactants
Neg delta H value
Endothermic reaction facts
When heat is absorbed
Heat content of products is greater than reactants
Bonds in reactants are stronger than the bonds in products
Pos delta H value
Kinetic Molecular Theory of Gases
Gases are made up of particles moving constantly and at random.
Gas particles are very far apart, and the volume of the particles is very small compared with the volume that the gas occupies.
The forces of attraction and repulsion between gas particles are zero.
Gas particles collide with each other and the walls of their container, exerting pressure.
The higher the temperature, the faster the gas particles move, increased kinetic energy.
Kinetic Molecular theory statement
Matter is made up of continuously moving particles
Gas Pressure definition
Particles exert a force by colliding with the walls of a container. Each tiny collision adds to all the others to make up the continuous force
Pressure equation
Pressure = Force / Area
Unit of measurement of pressure
Pascals
1 kPa = 1000 Pa
Unit of temperature
Kalvin
Temperature (c to K)
K = c + 273
Volume of gas conversions
1 m^3=10^3 L=10^6 mL
Boyle’s Law
Pressure is inversely proportional to volume
P1V1=P2V2
Charles Law
Volume is proportional to temperature
V1/T1 = V2/T2
Combined Gas equation
P1V1/T1=P2V2/T2
Molar Gas Volume Theory
Equal volumes of all gases measured at the same temperature and pressure contain the same number of particles
Molar Gas Volume Value
1 mole of any gas at SLC occupies a volume of 24.8 L
Formula for mol of Gases
n = V/Vm
V is in L
Vm is 24.8L/mol
Universal gas equation
PV=nRT P=pressure V= volume in L n= mol R=8.31JK^-1mol^-1
Mass conversions
1 tonne = 1000kg = 1000000g
Calculating greenhouse gases from 1 MJ of energy
- If the mole of the fuel produces a particular amount of kJ, convert MJ to kJ and cross multiply to find mole
- Work out ratio between fuel and greenhouse gas (CO2), and find mol for CO2
- Use n=V/Vm to work out volume of CO2
or use n=mXM to work out grams