Week 8/9 Flashcards
What does the occurrence of temperature change indicate?
That energy has changed form
What evidence will chemical change usually produce?
A gas produced A precipitate is formed A permanent colour change An apparent change in mass A temperature change
What may be needed for a reaction to occur or what may be produced as a result of the reaction?
Energy
What happens to the bonds when a reactions occurs?
Some bonds are broken and some are formed.
If less energy is stored in the products then was present in the reactants, then what happens?
The surplus energy is released as heat.
What do all molecules contain? Where is it contained?
Stored chemical energy
Contained within the bonds that are between the atoms that are within the molecules and within the the bonding between the molecules themselves.
What is the stored chemical energy called and what is its symbol?
Enthalpy or heat content
H
Formula for the change in enthalpy?
△H = H products - H reactants
*△H = change in enthalpy
What happens in an endothermic reaction?
△H is +
E products > E reactants
Heat energy added to the reactants (absorbed)
What happens in exothermic reactions?
△H is -
E reactants > E products
Heat energy released by reactants
What will often happens to the surrounding temperature during an exothermic reaction?
It increases
Eg of endothermic reactions?
Photosynthesis, evaporation of water, backing bread
Eg of exothermic reactions?
Lighting Bunsen burner, rust, formation of snow in clouds
Define redox reaction?
A chemical reaction that involves the transfer of electrons either by gaining or losing them
What is involved in oxidation?
Gain of oxygen
Loss of hydrogen
LOSS OF ELECTRONS