Enthalpy Change
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What is the exothermic reaction & it’s ΔH sign
ΔH- Heat loss to surrounding
What is the endoothermic reaction and it’s ΔH sign
ΔH+ Heat absorbed from surrounding
What is Activation energy
The minimum energy required for a reaction to take place
What are the 3 standard conditions for ΔH
298K 100kPa Solution at 1mol
What is standard enthalpy change of a reaction ΔrH
The enthalpy change for a given equation
What is standard enthalpy of combustion ΔcH
The enthalpy change when 1 mol of substance completely combusted at 298K and 100kPa
What is standard enthalpy of neutralisation ΔneutH
The enthalpy change when 1 mol of H2O is formed from the neutralisation reaction of H+ and OH- at 298K and 100kPa
What is standard enthalpy of formation ΔfH
The enthalpy chnage when 1 mol of compound is formed from it’s element at 298K and 100kPa
What is the apparatus that determines ΔH in a lab called
Calorimetry
What are the 2 equations used to calculate ΔH
q = mcΔT ΔH = -q/1000 / n
What are the 2 methods of calorimetry
• Combustion • Reaction in a solution
Why is the result of ΔcH is different to data book
-Heat loss to surrounding - Incomplete combustion - Evaporation of alcohol/ water
Why is the result of ΔrH is different to data book
• Heat loss to surrounding / Heat gained from surrounding • Incomplete reaction • Water evaporates from beaker
What stays the same even the same reaction is carried out with different amount of reactants
ΔH
What is changed if the amount of substance doesn’t affect ΔH
q, n, m, ΔT
Structure of predcting Temp change. questions
q= n x ΔH ΔH is the same n is ______ so q is ______ q= m c ΔT so m is _____ so ΔT is _______
What is average bond enthalpy
The enthalpy change for the brekaing of 1 mol of bonds in gaseous molecule
The more positive the bond enthalpy, the ______ the amount of energy needed to break the bond, so the _______ the bond
larger , stronger
Bond enthalpy (ΔBEH) are _________ (endo or exo)
Endothermic
Why are bond enthalpy always endothermic
As breaking bond always requires energy and making bond always releases energy (BENDO MEXO)
If a reaction is endothermic (ΔH+) meaning the energy required to break the bond is ____ than the energy realeased when making the bond
greater
If a reaction is exothermic (ΔH-) meaning the energy required to break the bond is ____ than the energy realeased when making the bond
less
What’s the equation for using Bond enthalpy to calculate ΔH
Σ Bond broken - Σ bond formed (BF)
Why is it not always possible to measure enthalpy change
• Very high activation energy • Very slow rate of reaction • Side reactions