Enthalpy Changes Flashcards
Endothermic reactions
Enthalpy of products> enthalpy of reactants
System absorbs heat from surroundings: More energy taken in making bonds, than released breaking bonds.
Give +/ve values
Exothermic
Enthalpy of products
System
Reactant and products
Surroundings
Environment outside chemical system
Standard enthalpy change of reaction (3)
Standard conditions
Reactants and products in standard state
Molar quantities as expresses in chemical equation
Standard enthalpy change of combustion (4)
Complete combustion
1 mole of substance reacts completely with O2
Standard conditions
Reactants and products in standard states
Standard enthalpy change of formation (3)
1 mol of product is formed
Standard conditions
Reactants elements in natural states
Standard enthalpy change of neutralisation (3)
1 mol of water formed in acid-base neutralisation
Standard conditions
Usually -57 KJmol-
Enthalpy
Heat contender stored in chemical system
Activation energy
Minimum energy required to start a reaction by breaking of bonds
Atom economy
(Sum of molar masses of desired products) x (sum of molar masses of all products)
Average bond enthalpy
The average enthalpy change that takes place when breaking;
- by homolytic fission
- 1 mol of a given type of bond in the molecules of a gaseous species.
What is the formula for finding how much heat has been transferred in a reaction?
Q= Mc🔺T
Mass of surroundings x specific heat capacity x difference in temperature
Formula for enthalpy change
-Q/ n
Heat transferred/ number of moles
What are the standard conditions
- 298K
- 101 kPa
