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Module 3 - Chapter 9 - Enthalpy I - Coggle Diagram
Module 3 - Chapter 9 - Enthalpy I
Enthalpy changes
Enthalpy is a measure of the heat energy in a chemical system (atoms/ molecules/ ions that make up chemicals
Energy stored within bonds
Difference in enthalpy = Enthalpy of products - enthalpy of reactants
Conservation of energy
Energy cannot be created or destroyed
Heat energy is transferred between the system and the surroundings
Determining
Enthalpy canges can be determined by measuring the energy transfer between the system/ surroundings
Exothermic - from the system to the surroundings
Endothermic - from the surroundings to the system
Exothermic
Chemical system releases heat enegry to surroundings
Enthalpy change is negative
Surrounding temperature increases
Energy loss by chemical system is balanced by energy gain of the surroundings
Endothermic
Chemical system takes in heat energy from surroundings
Energy gain by chemical system is balanced by energy loss by surroundings
Enthalpy change is positive
Surrounding temperature increases
Activation energy
Minimum energy required for a reaction to take place
Standard enthalpy change
is an enthalpy change under standard conditions
Difference between reactants and top of the hump of an enthalpy profile diagram
Standard conditions
Standard temperature = 25 C (298K)
Standard concentration - 1 mold dm^-3
Standard state = physical state of substance under standard conditions
Standard pressure = 100 kPa
Enthalpy change of reaction
Enthalpy that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions
A reactants and products are in their standard states
refers to a stated equation, its value depends on the balancing numbers
Both values of
are correct, but only for the quantities given in each equation
Enthalpy change of formation
Standard enthalpy change of formation
is the enthalpy change that takes place when one mole of a compound is formed from tis elemebts under standard conditions, with all reactants/ products in standard states
Compounds
A factional equation can give the enthalpy change for the formation of 1 mol of a compound
Equation could have been written using whole numbers, but it wouldn't be the
, as it requires 1 mole of Mg0
Elements
refers to the formation of one mole of an element from its elemeNt, so all elemENts have an enthalpy change of formation of 0
Enthalpy change of combustion
Standard enthalpy change of combustion
, is the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, with all reactants and products in their standard states
Products are oxides of the elements in the substance
Equation could have been balanced without fractions, but it wouldn't match the definition
Enthalpy change of neutralisation
Standard enthalpy change of neutralisation
is the energy change that accompanies the reaction of an acid by a base to form one mole of H20 under standard conditions with all reactants/ products in standard states
Value of
is the same for all neutralisation reactions
