1.4 Energetics Flashcards
Exothermic definition
Energy is released from the chemical to the surroundings
Endothermic definition
Energy is taken in from the surroundings
Enthalpy change definition
The change in heat energy at constant pressure
What is the enthalpy change for exothermic processes?
Negative
What is the enthalpy change for endothermic processes?
Positive
What are the standard conditions?
100kPa
25C (298K)
1.0 mol dm-3 concentration
What happens to the bonds in a reaction?
The bonds in the reactants are broken
The bonds in the products are formed
What type of reaction is breaking bonds?
Endothermic as energy is required
What type of reaction is forming bonds?
Exothermic as it releases energy
Activation energy definition
The minimum energy needed to start a reaction
Mean bond enthalpy definition
The energy required to break one mole of covalent bond into gaseous atoms averaged over a range of different compounds
What type pf process is a mean bond enthalpy reaction?
Endothermic (positive)
Standard enthalpy of combustion definition
Enthaply change when one mole of substance is completely burnt in excess oxygen under standard conditions, all reactants and products in their standard states
What substances have a zero enthalpy of combustion?
Water and carbon dioxides
Why may the enthalpy of combustion be difficult to measure?
Incomplete combustion may occur
