Chemical Reactions Flashcards
(12 cards)
1
Q
when is a new substance formed
A
during a chemical reaction
2
Q
what describes most chemical reactions
A
not easily reversed ( irreversible )
3
Q
when is there no new substance formed
A
during a physical change
4
Q
examples of physical changes
A
melting and evaporating
5
Q
what describes physical changes
A
reversible
6
Q
when can you tell that a reaction has occurred
A
if there is a colour changes or a gas given off
7
Q
what do most chemical reactions involve
A
an energy change
8
Q
what is an energy change usually in the form of
A
heat but can involve light or sound being given of
9
Q
example of energy change
A
when something burns
10
Q
what else do some chemical changes involve
A
decomposition
11
Q
what is decomposition
A
chemicals being split up
12
Q
what does decomposition need
A
a source of energy, usually heat or electricity
