Enthalpy Flashcards
Definition of enthalpy
The heat content stored in a chemical system
Exothermic reaction
A reaction in which heat is lost to its surroundings
The enthalpy of the products is lower than the reactants made
Endothermic reaction
A reaction in which heat s taken in from the surroundings
The enthalpy of the products are higher than the enthalpy of the reactants
How does a self heating can work using calcium oxide and water
The calcium oxide and water are separated by a barrier
Pull a ring you separate barrier, the 2 compounds REACT
releasing heat
Examples of exothermic reactions
Oxidation/ combustion
RESPIRATION
eXAMPLES OF endothermic reaction
photosynthesis
thermal decompositon
Definition of an enthalpy profile diagram
Diagram for a reaction to compare the enthalpy of the REACTANTS with the enthalpy OF THE PRODUCTS
x AND Y AXIS OF ENTHALPY PROFILE DIAGRAM
X- progression of reaction
Y- enthalpy
Activation energy
Minimum energy required to start a reaction by BREAKING BONDS
wHAT are standard condition
1 Atm
250c
1 molddm-3
wHAT IS MEANT BY STANDARD STATES
The physical state of a substance under STANDARD CONDITIONS
Definition of the standard enthalpy change of reaction
The enthalpy change that takes accompanies a reaction when molar quantities of reactants of products as expressed in the equation react under stanadard conditions all being in their standard states
Standard enthalpy of combustion
The enthalpy change that takes place when one mole of a FUEL is burned COMPLETELY in oxygen under standard condition, all products and reactants being in their standard states
Standard enthalpy change of formation
The enthalpy change that takes places when ONE MOLE of a compound is formed from its constituent elements in their standard states, under standard conditions
Specific heat capacity
The energy required to raise the temperature of of 1g of a substance by 1 degree c
An experiment to measure SHC
Calorimetry
Process of finding enthalpy change using Q=Mdelta T
Find Q by subbing
find amount in moles that was reacted
Divide by 1 to work out KJ/mol
Two theoretical methods of calculating enthalpy
Mean bond dissociation
Enthalpy cyccle
Describe the experimental method to determine the enthalpy change of combustion for a fuel
Burn a known mass of a substance in air
Heat up a n=know mass of water
measure temperature change in water
WHy is there a difference between the the experimental value and the standard value
Incomplete combustion
Heat may be lost to surroundings
To get a better agreement of an experiemental enthalpy change what can you do
Cut down on heat loss
Ensure complete combustion
How is a bomb calorimeter a better way of measuring
Ensures fuel burns in complete combustion
Heat is transferred to water…welll insulated… reduces heat loss to surroundings
;Bond enthalpy defintion
The enthalpy change that takes place when breakind by HOMOLYTIC FISSION 1 mol of a given bond in the molecules of a GASEOUS SPECIES
Average bond enthalpy
The avverage enthalpy change that takes place when one mole of a given bond is broken by HOMOLYTIC FISSION
IN THE MOLECULES OF A GASEOUS SPECIES
