Enthalpy changes

Exothermic reactions can be identified by detecting a temperature ...

increase

Endothermic reactions can be identified by detecting a temperature ...

decrease

breaking bonds ... energy

absorbs

forming bonds ... energy

releases

intermolecular and covalent bond breaking is ...

endothermic

forming bonds is ...

exothermic

What is the definition of an exothermic reaction?

when more energy is released in bond making/forming than is absorbed in bond breaking

MEXO BENDO

What is the definition of an endothermic reaction?

when more energy is absorbed during bond breaking than is released during bond formation.

MEXO BENDO

What is the activation energy?

the minimum energy required for a reaction to occur

Activation energy is ALWAYS ...

positive

An exothermic diagram profile:

An endothermic diagram profile:

What is the definition for the standard enthalpy of formation?

formation of 1 mol of a compound from its elements

What is the definition for the standard enthalpy of combustion?

complete combustion of 1 mol of a substance

What is the definition for the standard enthalpy change of neutralisation?

formation of 1 mol of water from neutralisation

What is the definition for the standard enthalpy of reaction?

enthalpy change associated with a stated equation

What type of enthalpy change is ?

enthalpy change of formation

What type of enthalpy change is ?

enthalpy change of combustion

What type of enthalpy change is ?

enthalpy change of formation

What type of enthalpy change is?

enthalpy change of neutralisation

Why might practical ΔH values be less exothermic than database values? Give 3 reasons

• heat loss to the surroundings

• incomplete combustion

• none standard conditions used

Which is Ea and ΔH