C7- Energy changes Flashcards
Conservation of energy meaning
Energy is conserved in reactions, neither created nor destroyed
Exothermic reaction including energy and bonds?
A reaction that releases energy to the surroundings. Releases more energy by forming bonds than is needed to break bonds.
Endothermic reaction including energy and bonds?
A reaction that absorbs energy from the surroundings. Requires more energy to break bonds than it releases by forming bonds.
How to investigate temperature changes
Measure substances into a polystyrene cup, place lid with thermometer through it, record initial temp and calculate temp change
2 uses for exothermic reactions
Hand warmers and self heating cans
1 use for endothermic reactions
Instant cold packs
What are the typical reactants in self-heating cans
Calcium oxide+water
What are the typical reactants in instant cold packs
Ammonium nitrate dissolved in water
What does a reaction profile show?
Relative energies of the reactants and products
Exothermic reaction profile
Products level?
Energy transferred to..?
Products at a lower level than reactants
Energy transferred to surroundings
Endothermic reaction profile
Products level?
Energy transferred to..?
Products at a higher level than reactants
Energy absorbed from surroundings
Activation energy
Minimum amount of energy needed for particles to successfully collide
Endothermic form/break bonds?
Breaks bonds, requires energy
Exothermic form/break bonds?
Forms bonds, releases energy
Bond energy
Definition?
Unit?
Key fact?
Energy required to break the covalent bond between two atoms
kJ/mol
Always greater than 0
