energetics(both) Flashcards
what are the standard conditions?
100kpa
298k
what is a formation reaction?
when one mole of a substance is formed from its constituent elements
give the formation reaction for ammonia
1/2N2+ 1 1/2 H2= NH3
define enthalpy change
heat energychange of a reaction at constant pressure
what are the two elements that are liquid under standard condtions?
- bromine
- mercury
how do you calculate the enthalpy change using mean bond enthalpy?
total energy to break bonds- total energy released from forming bonds
define mean bond enthalpy
an average value for the bond enthlpy of a particular bond over the range of compounds it is found in
what is calorimetry used for?
enthalpy change of combustion
what is the units for enthalpy change
KJmoldm3
what calculation is used to work out the energy from a calorimetry experiment?
q=mc deltaT
what are the different components of the q= mc delta T equation+give units
q= heat energy lost/gained J
m= mass of water/solution being heated
c= SHC of water g-1K-1
t=temperature change K
100g of water was heated from 23 degrees to 57 degrees by 1.8g of ethanol. calc the energy transferred and hence the enthalpy change of the fuel
14212J or 14.212KJ=q
enthalpy= q/moles
enthalpy=-364.4KJmol-1
what can calorimetry be used for?
calculating energy change from a calorimetry experiment of a solution or fuel
What is the units for Enthalpy?
KJmoldm-3
Why is it important during RP 2 that the mixture is stirred before recording each temperature
Ensure all solution is at the same temperature to give an accurate reading
what is hesss law?
the total enthalpy change of a reaction is independent of the route taken
draw the formation cycle
draw the enthalpy of combustion cycle
what do you do during hess’ cycles if there is reactants and products that are exactly the same and the same amount of moles
do not need to include these in the calculation because they will cancel each other out
how do you check if your hess’ cycle calculations are correct?
go along the cycle and add all values it should add to 0
what is the calculation for enthalpy change?
total energy absorbed- total energy released
define standard enthalpy of combustion
the enthalpy change when 1 mole of a substance is burnt completely in oxygen with all all reactants and products in their standard states and under standard conditions
define standard enthalpy of formation
enthalpy change when 1 mole of a compound is formed from its constituent elements with all reactants and products
in their standard states under standard conditions
define standard enthalpy change of reaction
the enthalpy change when a reaction occurs in molar quantities shown in the chemical equation under standard conditions with all reactants and products in their standard states
