Obtaining energy from fuels Flashcards
Gases
Define gas
The gas is a state of matter whereby the individual particles (wherever there may be single atoms or molecules) are widely spaced apart and are moving independently of one another
Gases
Volume and pressure
The pressure in the vessel is equal ….
to the force of the gas on the wall of the vessel, per unit surface area with the standard unit being the Pascal (Pa)
Gases
Volume and pressure
Where does the force come from?
Remember that the particles in the vessel are moving in random directions repeatedly coiling with the wall of the vessel and trying to push the vessel outwards
Gases
Relationship between pressure temperature and amount and volume
At a given temperature and pressure …
the amount of gas molecules in a vessel is proportional to the volume of the vessel. This is known as Avogadro’s Law
Gases
Relationship between pressure temperature and amount and volume
At the same temperature and pressure…
The amount of gas molecules in each vessel is the same
Gases
Relationship between pressure temperature and amount and volume
The equation pV = nRT, stands for
P = pressure in kPa V = volume in L n = total amount of gas molecules (in mol) in the vessel R = universal gas constant in 8.31 T = temperature in Kelvin
Gases
Standard molar volume
STP (standard temperature and pressure)
Temperature at 0°C (273 K) and a pressure of 1 bar (100kPa)
molar volume is 22.7 L mol-1
Gases
____
°C °K
____
+ 273
-273
Gases
Standard molar volume
SLC (standard laboratory conditions)
Temperature at 25°C (298 K) and a pressure of 1 bar (100kPa)
molar volume is 24.8 L mol-1
Gases
Relationship between pressure temperature and amount and volume
Whats Boyle’s Law
Increasing the volume of the decreases the pressure inside the vessel expanding the volume of the particles spread out more and therefore collide less frequently with the sides of the vessel and vice versa
Gases
Volume and pressure
mm —> kPa
Hg
/760 x 101.3
760 x 101.3 /
Gases
Volume and pressure
Pa —> kPa
/1000
x1000
Gases
Volume and pressure
atm —> kPa
/101.3
x101.3
Gases
Volume and pressure
bar —> kPa
x100
/100
Gases
Volume and pressure
–>
ug, mg, g, kg, t
/1000
x1000
Energy profiles
The energy profile depicts the energy changes that occurs during a chemical reaction
Energy profiles Chemical energy (also known as enthalpy)
This is the energy contained within the various electric forces within and between species. The symbol for enthalpy is ΔH
Energy profiles
Thermal energy
this is what we often think as heat. It is the kinetic energy that manifest in the speed of randomly moving particles. The higher the thermal energy contained within the set of molecules, the higher their speed and therefore the higher the temperature of the system
Energy profiles
Kinetic energy
This is the umbrella term for energy contained within the movement of particles. Thermal energy is a type of kinetic energy
Energy profiles
Steps that occur throughout the reaction
- The reactant particles move closer to one another
- The reactant particles move close enough to another for their electrons to start repelling one another, slowing the particle down. The kinetic energy for the particles is being converted into the chemical energy. Here the empathy starts to rise
- The reactant particles collide and the reactant bonds break. Breaking of bonds require energy to be ‘injected’ into the chemical. Hence the enthalpy continues to rise
- New bonds create the products. The formation of new bonds causes a decrease in chemical energy and conservation into kinetic energy. Hence the enthalpy will fall.
Energy profiles
Draw exothermic and endothermic energy profile.
DO IT
Energy profiles
Define activation energy
is the minimum energy needed to commence the reaction. It is discipline by EA on an energy profile and is sourced from the kinetic energy of the moving reactant particles
Energy profiles
Define change in enthalpy
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-
- If ΔH is positive. then this means that the reaction is endothermic, usually decreasing the temperature of the surroundings
- If ΔH is negative the reaction is exothermic. There has been an release of energy by the reaction is usually increasing the temperature of the surroundings
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- If you want to multiply the coefficient of a reaction by x, then multiply ΔH by x
- If you want to add two equations together, add their ΔH values
- If you want to reverse the direction of a reaction, change the sign of the ΔH value
