Enthalpy change

What kind of reaction is associated with bond breaking

Endothermic

What kind of reaction is associated with bond making

Exothermic

What do all chemical reactant shave a certain amount of

Stored chemical energy

Enthalpy definition

Thermal energy stored in a system

What is a system

Atoms and bonds involved in the chemical reaction

What can Enthalpy change be monitored by

Temperature change

Symbol for Enthalpy change

Triangle H

Exothermic reaction features

Products have less energy than the reactants, energy is given out to surroundings, temperature of surroundings increases

Endothermic reaction features

Products have more energy than the reactants, energy is taken in from surroundings, temperature of surroundings decreases

Endothermic energy level diagram

Products energy level is higher than the reactants as heat has been taken in

Exothermic energy level diagram

Energy level of products is lower than reactants as heat is given out

Enthalpy change definition

Heat exchanges with. He surroundings during a chemical reaction, is the difference between the energy of the products and the Enthalpy of reactants

Enthalpy change equation

Enthalpy change = Enthalpy products - Enthalpy of reactants

What does theta mean

Standard conditions

What is Enthalpy change measure in

KJ/ mol

Standard conditions

100 kPa, 298 Kelvin, 1 mol/dm³ concentration

Standard state definition

The physical state of that substance under standard conditions eg water = liquid

Activation energy

Ea = minimum energy required for a reaction to take place

Exothermic Enthalpy profile diagram

Products below reactants

Endothermic Enthalpy diagram

Enthalpy of products is higher than reactants

What do you need on Enthalpy profile diagrams

State symbols, all arrows point upwards

Enthalpy of formation symbol

Triangle H subscript f

Enthalpy change definition

When one mole of a substance is made from its constituent elements in their standard states under standard conditions

Enthalpy o formation of CH4

C(s) + 2H2(g) → CH4 (g)

What do you need to do when writing Enthalpy of formation equations

Balance so you get one mole of product, use state symbols

What is the ^Hf for any element in its standard state

0 as the element has already been formed so there’s no change in energy

Diatomic molecules

Hydrogen, Nitrogen , Fluorine, Oxygen, Iodine, Chlroine, Bromine → Have No Fear Of Ice Cold Beer

Enthalpy change of combustion symbol

Triangle ^ H subscript c

Enthalpy change of combustion definition

Enthalpy change when one mole of a substance us burned completely in oxygen under standard conditions

^Hc of CH4

CH4 (g) + 2O2(g) → CO2 (g) + 2H2O (l)

What do you need in equations for ^Hc

State symbols, one mole of named compound eg chlorine

Enthalpy change of neutralisation symbol

Triangle ^ H subscript neut

^Hneut definition

Enthalpy change when one mole of water is formed during a neutralisation reaction under standard conditions with all reactants and products in their standard states

^Hneut of HCl

HCl (aq) + NaOH(aq) → NaCl(aq) + H2O(l)

What do you need in equations for ^Hneut

State symbols, one mole of water in products

Ionic equation for neutralisation ractions

H+ + OH- → H2O

Trick to work out equations for ^Hneut

Only need one lot of H+ ions so for things like H2SO4 you can quickly see you only need half eg ½ H2SO4 (aq) + NaOH(aq) → H2O (l) + ½ Na2SO4

Enthalpy change of reaction symbol

Triangle H subscript r

^Hr definition

Enthalpy change when the number of moles of reactants specified by the balanced equation react together

How can ^Hr, ^Hc, ^Hneut be measured

Through an experiment using a thermometer