Types of enthalpy change

What is enthalpy H Of a system

A measure of the energy stored in ( or heat content of ) a system. It can’t be measured directly.

What is the enthalpy change in 🔺 H ‘ delta H ‘ ?

The energy being neither given out or taken in during a reaction . As the enthalpy of the reactant / product is not the same

Enthalpy change

The amount of heat energy taken in or given out during any change in a system in standard conditions and given the symbol 🔺

What is the definition of standard state ?

Physical state of a substance under standard conditions. most data table show the standard state at 100 KPa and 298 K

What the the conditions for a standard enthalpy change ?

Temp : 298 K

Pressure : 100 KPa

Con.c ; 1.0 mol dm -3

What are the equation for the standard enthaply change

🔺H * = H* products - H * reactants

Units : KJ mol -1

Defining specific 🔺H * values :

Al such definitions follow the same format involving.

1) quantity of arterial - one mole

2) Process - formation , combustion , atomization

3) conditions - stated temp ( 298 K / 100 KPa)

Energy level diagrams

H products < H reactants → H 🔺 negative

Exothermic reaction - level diagram

Energy of reaction - negative, energy content of the system - decreased

Some energy left the system and entered the surrounding as heat

Net decrease in the potential energy of the system

Endothermic reaction - level diagram

Energy of reaction - increase , energy content of the system - increased

Some energy entered the system and loss to the surrounding as heat

Net increase in the potential energy of the system

Enthalpy change of reaction - 🔺Hr *

Enthalpy change of reaction in the molar quantities shown in chemical reaction under standard conditions with all reactants + products in their standard state

Example of enthalpy change of reaction

H2SO4 ( aq ) + 2 NaOH → Na 2 SO4 ( aq ) + H2O ( I )

H2 ( g ) + ½ O2 ( g ) → H2O ( I ) = - 286 kj mol-1

The enthalpy change of combustion

The standard enthalpy change of combustion 🔺He * is the enthalpy change that take place when one mole of a substance reacts completely with O2 under standard conditions, all reactant / product being in their standard state.

Example of enthalpy change of combustion

C2H6 ( g ) + 3 ½ O2 ( g ) → 2 CO2 ( g ) + 3 H2O ( I ) = - 1560 Kj mol -1

enthalpy change of formation

The standard enthalpy change of formation 🔺Hf* is the enthalpy change that take place when 1 mole of compound is formed from its elements in their standard state under standard conditions.

Example of enthalpy change of formation

H2 ( g ) + ½ O2 ( g ) → H2O ( I ) 🔺HF * = - 286 Kj mol -1

enthalpy change of neutralization

The standard enthalpy change of neutralization 🔺 neut H* is the energy change that accompanies the reactions of an acid by a base.

Example enthalpy change of neutralization

HNO3(aq) + ½ Bа(OH)2(aq) → ½ Ba(NO3)2(aq) + H20(()

½ H2SO4(aq) + ½ Ва(ОН)z(aq) → ½ BaSO4(s) + H20(I)