What are the 2 changes
Endothermic and exothermic
What’s exothermic change
Where heat is released / given out to the suroundings
What’s endothermic change
Where heat is taken in / absorbed from surroundings
Graph for exothermic change (temp)
Start from room temp then reach max temp then decrease to start n stay equal
Describe graph for exothermic change ( temp)
- when (compound) react with ( another compound) , heat energy is GIVEN OUT to surroundings , INCREASE in temp
- MAX temp is reached during COMPLETE reaction
- temp DECREASES as RESULTING mixture COOLS
- temp returns to ROOM TEMP
Graph for endothermic change (temp)
Decrease from starting temp to room temp then increase to start temp n stay the same
Describe graph for endothermic change ( temp)
- ( compound) dissolves in water, heat energy take in from surroundings , decrease temp
- minimum temp reached when (compound) completely dissolved
- temp increase as resulting mixture takes in heat from surroundings
- temp returns to same as room temp
Which processes are exothermic ( physical)
Freezing
Condensation
Crystallisation
Which processes are endothermic ( physical)
- boiling
- evaporation
- melting
- sublimation
Which chemical reactions are exothermic
- neutralisation of reaction
- respiration
- combustion of fuels
- reaction of acid w metals
Chemical reactions that are endothermic
- thermal decomposition of compounds
- photosynthesis
Energy level diagram for exothermic reaction
Energy level of products is lower than energy level of reactants
Why is there a diff in energy level for exothermic reactions
Its the energy given out to surroundings during reaction
ENERGY CHANGE IS NEGATIVE
What’s the energy level diagram for endothermic reaction
Products have a higher energy level than reactants
Why is there a diff in energy level in endothermic reactions
- energy taken in from surroundings
ENERGY CHANGE IS POSITIVE
Process of bond breaking and bond forming in chem reaction
- reacting particles must collide w eo
- bonds in reactants go thru bond breaking ( endothermic change)
- new bonds btwn atoms form , go thru bond forming ( exothermic change)
What is enthalpy change
Overall heat change in a reaction
What’s the symbol and unit for enthalpy change
Symbol : a triangle n a H
Units : kJ
Why is enthalpy change in exothermic reaction negative
Energy RELEASED during bond forming in products is MORE than the energy ABSORBED during bond breaking in reactants
Grah for bond forming n breaking (exothermic)
Start from the mid
Increase ( bond breaking)
Decrease to below start point ( bond forming)
THUS THE ENTHALPY CHANGE IS NEGATIVE
Graph for bond breaking n forming (endothermic)
- low starting point
- increase v high ( bond breaking)
- Decrease to btwn start n v high ( bond forming)
THUS ENTHALPY CHANGE OF ENDOTHERMIC IS POSTIVIE
Why is enthalpy of endothermic change POSTIVE
Energy RELEASED during bond forming in products is LESS than energy ABSORBED during bond breaking in reactants
Energy profile diagrams for exothermic reaction
- start from mid
- increase ( curved)
- decrease ( v steep down)
- constant
What to label for energy profile diagrams
- reactants
- Ea ( the dist from reactant level to max at curve)
- enthalpy change ( use unit) –> from the reactant level to product levell
- products
