IB chemistry : R.1.1 - measuring enthalpy changes

i have flopped :(

mean bond enthalpy definition

• the energy required to break 1 mol of bonds in gaseous covalent molecules

• under standard conditions

• the diatomic elements in enthalpy equations end up monoatomic

• it’s an average value for all the bonds in many different bonds

bond enthalpy energy

The average enthalpy change required to break a specific bond between two elements in a molecule, measured under standard conditions

endothermic reactions

• the product absorbs energy

• so the enthalpy increases

• the products are less stable than the reactants

• happens when bonds are broken ( because energy is required to break the bonds. eg l → g )

exothermic reaction

• the product releases energy

• the enthalpy decreases

• products are more stable ( don’t have as much energy )

• happens when bonds are formed

formula for a heat change

Q = temperature change x C x moles of reactant

when exothermic, it’s negative

heat is energy, not temperature