energy is released from the system into the surroundings, Heat EXITs (leaves the system)
products are lower in energy than the reactants (because energy has been released)
An endothermic reaction occurs when
energy is absorbed by the system from the surroundings, Heat ENTERS (goes into the system)
products are higher in energy than the reactants
Delta H is negative for exothermic reactions (since products are lower energy than reactants)
Delta H is positive for endothermic reactions (since products are higher energy than reactants)
Delta H is the difference between the energies of the products and reactants
Activation Energy, is the energy necessary to start the reaction, used to break bonds or intermolecular forces in the reactants
Catalysts are added to reactions to increase the reaction rate. They are not consumed in the reaction. Some catalysts provide an alternate pathway with lower activation energies. Delta H is NOT changed by a catalyst
Combustions are exothermic reactions
All decompositions are endothermic reactions
Photosynthesis is an endothermic reaction
Standard Conditions:
101 kPa or 1 atm
298 K or 25 C
Strong Acids:
HCl
HBr
HI
HNO3
H2SO4
Strong Bases:
NaOH
KOH
Ca(OH)2
Ba(OH)2
Sr(OH)2
Bond breaking is endothermic
Bond forming is exothermic
If more energy is required to break bonds than energy is released when new bonds are formed, the reaction is endothermic
If more energy is released when new bonds are formed than energy is required to break bonds, the reaction is exothermic.
The amount of energy required to break one mole of a specific covalent bond in the gas phase is called the bond dissociation energy.
Neutralizations or acid-base interactions are exothermic
Enthalpy Change - the energy exchange between a chemical reaction and its surroundings at constant pressure is called the enthalpy change
Enthalpy - the total energy associated with the materials that react
Activation Energy - the minimum energy that colliding particles must possess for a reaction to happen
Standard enthalpy change of reaction - the enthalpy change when the amount of reactants shown in the stoichiometric equation react to give products under standard conditions
Standard enthalpy change of formation - the enthalpy change when one mole of a compound is formed from its elements under standard conditions
Standard enthalpy change of combustion - enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions
Standard enthalpy change of neutralization - enthalpy change when one mole of water is formed by the reaction of an acid with an alkali under standard conditions
Specific heat capacity - the energy required to raise the temperature of 1 g of a substance by 1 degree C (1 K)
Specific heat capacity of water is 4.18 J g-1 C-1
Hess's law - the states of the reactants and products must also be the same whichever route is followed