holy smokes im cooked

temperature

a measure of the average kinetic energy of the particles

heat

measure of the energy content of a substance

system

inside reaction vessel

surroundings

outside the reaction vessel

enthalpy

The total chemical energy inside a substance

Exothermic reactions

when products have less enthalpy than reactants, and heat is released

• Heat energy is given off by the system to the surroundings

  • The temperature of the surroundings increases

  • The temperature of the system decreases

endothermic

when products have more enthalpy than reactants. heat is absorbed

• The temperature of the surroundings decreases

• The temperature of the system increases

transition state

unstable state. chemical bonds are partially broken and formed

activation energy (E_a)

• The activation energy is the energy difference from reactants to transition state.

‘the minimum amount of energy needed for reactant molecules to have a successful collision and start the reaction’

The standard enthalpy change

• heat transferred at constant pressure under standard conditions and states

• These standard conditions are:

  • A pressure of 100 kPa

  • A concentration of 1 mol dm^-3 for all solutions

  • Each substance involved in the reaction is in its standard state (solid, gas or liquid)

standard enthalpy change of Reaction

The enthalpy change when the reactants in the stoichiometric equation react to give the 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

The enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions

exothermic

standard enthalpy change of neutralization

The enthalpy change when one mole of water is

formed by reacting an acid and alkali under standard conditions

exothermic

assumptions of calorimetry experiments in solution

• That the specific heat capacity of the solution is the same as pure water, i.e. 4.18 J g^-1 K^-1

• That the density of the solution is the same as pure water, i.e. 1 g cm^-3

• The specific heat capacity of the container is ignored

• The reaction is complete

• There are negligible heat losses

how to minimize heat loss in combustion calorimetry

lid and dont place too far

When bonds are broken or made

enthalpy changes take place

exothermic overall enthalpy change

• If more energy is released when new bonds are formed than energy is required to break bonds, the reaction is exothermic

  • The products are more stable than the reactants

endothermic overall enthalpy change

• If more energy is required to break bonds than energy is released when new bonds are formed, the reaction is endothermic

  • The products are less stable than the reactants

avg bong enthakpy

• 'The energy needed to break one mole of bonds in a gaseous molecule averaged over similar compounds

Bond enthalpy calculations formula

hess’s law

Hess's Law states that the enthalpy change for a chemical reaction is independent of the route taken. as long as reactants and products are the same

Enthalpy changes using enthalpy of formation

Enthalpy changes using enthalpy of combustion

ΔH^Ꝋ  = ∑ΔH_c^Ꝋ(reactants) - ∑ΔH_c^Ꝋ(products)

Born-Haber Cycles

application of hess law that finds lattice enthalpy

Lattice Enthalpy

atomization

ionization

electron affinity