5.2 - Energetics Flashcards
Exothermic reaction
Transfers energy to surrounds so temp of surroundings increases
E.g. combustion/neutralisation
E.g. handwarmers
Endothermic reactions
Takes in energy from surrounds so temp of surrounds decreases
E.g. thermal decomposition
Exothermic or endothermic: salt dissolving in water
Endothermic
Exothermic or endothermic: neutralisation
Exothermic
Exothermic or endothermic: displacement
Exothermic
Exothermic or endothermic: combustion
Exothermic
Heat energy change equation or enthalpy change
Q=mc🔼T
Heat energy change = mass of water x SHC x change in temp of water
How to convert J to kJ
divide by 1000
Moles
Mass/RFM
Q/kJ divided by mol =
Enthalpy change or kJ/mol
Exothermic reaction energy level diagram
Reactants have more energy -> goes down
Endothermic reaction energy level diagram
Reactants have less energy than products -> goes up
Energy needed to BREAK > energy released
Endothermic
Energy need to BREAK < energy released
Exothermic
What reversible reactions occurs in a closed system/sealed container
Equilibrium in reacts - reactions occurs at exactly same rate in each directions
Endothermic or exothermic: activating an ice pack
Endothermic
Endothermic or exothermic: thermal decomposition of CaCO3
Endothermic
Bond energy calculations
Enthalpy change = bond breaking - bond making = kJ/mol
Calculating enthalpy changes experimentally
- use chemical reaction to heat known mass of water
- measure temp of water before and after
- Q=mcAT
AH = -Q/mol
Errors of practical
- lots of heat lost to surroundings
- incomplete combustion (yellow flame/soot) produces less energy
What is SHC
4.2
Neutralisation
Acid reacts with alkali
Acid + base —> salt + H20
