Thermo chemistry Thermo chemistry The study of changes in heat The study of changes in heat

energy during chemical energy during chemical reactionreaction

ExothermiExothermic c

ReactionReaction

EndothermiEndothermic c

ReactionReaction

A chemical reaction that gives out or release of

heat energy to the surroundings

Exothermic ReactionExothermic Reaction

Chemical reaction that absorbs heat energy from

the surroundings

Endothermic Endothermic ReactionReaction

Energy Change During Energy Change During Formation And Breaking Of Formation And Breaking Of

Bonds Bonds Chemical Reaction :

bond breaking and bond formation

(absorb energy) (release energy)

If heat absorb to break the bonds higher than heat released during formation of bonds - endothermicendothermic

If heat absorb to break the bonds is lower than heat released during formation of bonds - exothermicexothermic

ENERGY LEVEL DIAGRAM ENERGY LEVEL DIAGRAM

Every chemical substances have certain amount of chemical

energy and different for different substances. Symbol is HHThe amount of heat energy released or

absorbed during chemical reaction heat of reaction.

Symbol is ΔΔHH, unit KJ mol KJ mol-1-1

ΔH = Total Energy Content Product – Total Energy Content Reactant

= Hproducts - Hreactants

The Energy Level Diagram For

Exothermic Reaction Endothermic Reaction

Reactants

Energy

Products

ΔH = - xKJmol-1

Reactants

Energy Product

s

ΔH = +yKJmol-1

APPLICATIONAPPLICATION

Separate compartment (thin film) of water + solid ammonium nitrate placed in a plastic bag

Squeezed it, the compartment broken and solid ammonium nitrate dissolved in water

Endothermic, provide instant coldness

Cold Pack

Separate compartment (thin film) of water + anhydrous calcium chloride placed in a plastic bag

Squeezed it, the compartment broken and anhydrous calcium chloride dissolved in water

Exothermic, release heat

Hot Pack

4 type of heat of 4 type of heat of reactions :reactions :

Heat of PrecipitationHeat of

NeutralizationHeat of DisplacementHeat of Combustion

HEAT OF PRECIPITATIONHEAT OF PRECIPITATION

m1

m2

DEFINATION :Heat of precipitation is the energy change

when 1 mole of precipitate is formedwhen 1 mole of precipitate is formed from its ions. To calculate Heat of PrecipitationStep 1 : find energy change , Q Q = mc m = m1 + m2 c = 4.2 = temp change

Step 2 : find mol, n both solution n = MV/1000

Step 3 : find H H = Q/ n KJ mol-1

-- - - - - - - -- - -

HEAT OF DISPLACEMENTHEAT OF DISPLACEMENT

DEFINATION :Heat of displacement is the energy change 1 1 mole of mole of

metal is displaced from its salt solutionmetal is displaced from its salt solution by more by more electropositive metalelectropositive metal

m

Excess metalTo calculate Heat of Displacement

Step 1 : find energy change , Q Q = mc m = m c = 4.2 = temp change

Step 2 : find mol, n solution n = MV/1000

Step 3 : find H H = Q/ n KJ mol-1

-- - - - - - - -- - -

HEAT OF NEUTRALISATIONHEAT OF NEUTRALISATIONDEFINATION :

Heat of neutralization is the energy change when 1 1 mole of watermole of water is formed from the neutralization between 1 mole of H+ ion from an acid and 1 1 mole of H+ ion from an acid and 1

mole of OH- ion from an alkali mole of OH- ion from an alkali

acidm1

Alkalim2

To calculate Heat of NeutralizationStep 1 :Step 1 : find energy change , Q Q = mc m = m1 + m2 c = 4.2 = temp change

Step 2 :Step 2 : find mol, n both solution n = mv/1000

Step 3 :Step 3 : find H H = Q/ n KJ mol-1

HEAT OF COMBUSTIONHEAT OF COMBUSTIONDEFINATION :

Heat of combustion is the heat given off when 1 1 mole of alcohol is burnt completelymole of alcohol is burnt completely in an excess

of O2 gas.

To calculate Heat of CombustionStep 1 : find energy change , Q Q = mc m = VOLUME OF WATER USED c = 4.2 = temp change

Step 2 : find mol, n (FOR FUEL/ ALCOHOL) n = Mass Of Alcohol Used Molar mass of AlcoholStep 3 : find H H = Q/ n KJ mol-1