(BLUE) Energetics 1 Flashcards
Draw a hess cycle using letters A-Y
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What is the study of energetics
The study of energy transfer between reacting chemicals and its products.
We measure the energy transfer to and from the surroundings as enthalpy change
What is the definition of enthalpy change for a reaction
: the heat change when the reaction is carried out at constant pressure pressure it gives the symbol (delta) H
What happens in an exothermic reaction , and what’s its symbol (+/-)
Energy is transferred to the surroundings , and energy levels for the compound go down so -Ve (delta) H is negative
What happens in an endothermic reaction and what sign(-/+)
Energy is transfers to the compound , therefore energy levels go up in the compound: +Ve (delta) H positive
Draw an enthalpy level diagram
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What is the equation of heat energy
Heat energy = specific heat x mass x (delta) temp (in kelvin)
What is the specific heat capacity of water
4.18 j kg-1
What are the units of enthalpy change
KJ mol-1
What is the definition of combustion enthalpy
(Delta) Hc
The heat energy when released when one mole of a substance in its standard state is completely burnt in excess oxygen understand reconditions ( 1 atm 298k)
What is the equation for 1 mil of (delta) H for one mole
(Delta)H = energy transferred / miles used
When carrying out combustion what else might get formed
On the tin can
Soot
List the main sources of heat loss:
Draughts
Heat absorbed from objects
Incomplete combustion
How does the number of carbons on a cain effect the enthalpy combustion
Would make it higher exothermic reactions
This is because more bonds are formed as more CO2 and H2O are formed
What is the definition of standers enthalpy change of formation
Enthalpy change when one mole of a substance in its standard state is formed from its elements in their standard states under standard conditions ( 1ATM 298k)
What is the definition of standard enthalpy change of reaction
The enthalpy change when molar quantities of reactants as stated in the equation react together under standard conditions (1ATM 298k 1mol dm-3)
The standard enthalpy change of neutralisation
The enthalpy change of neutralisation is the enthalpy change when one mole of water is formed by the neutralisation between an acid and an alkali under standard conditions (298k 1ATM)
How would you reduce heat loss when dealing with exo or endothermic reactions
Put a lid on it
Stirring
Weigh beaker before and after to measure the amount of compound used
To prevent liquids escaping from fizzing put a lid on it
Why can’t we measure (delta) Hr of
2NaHCO2 ——> Na2CO3 +CO2 + H2O
Because the reaction is endothermic , and we have to beat the compound in order to react which makes it harder / impossible to measure the (delta) Hr of this reaction
When bonds break is it exo/endo thermic
Endothermic
When bonds form is it exo / Endo thermic
Exothermic
What is the definition of dissociation enthalpy (also called bond enthalpy)
the energy required to break one mole of BONDS in a substance when it is the gaseous state
What is the difference between :
Bond dissociation enthalpy
And
Mean bond enthalpy
As enthalpy can change as you keep breaking bonds in a compound , mean bond enthalpy gives you a rough average . While bond dissociation enthalpy gives you exact numbers
Why is nitrogen (N2) Un reactive
Has a high bond dissociation enthalpy therefore needs a lot of energy to overcome
Give the equation for (delta) Hr
(Delta) Hr = total energy to break bonds - total energy to make bonds
