Chemical Reactions Flashcards
List 3 key signs of a chemical reaction
- A colour change.
- A flame or explosion.
- Reaction gets hot or cold by itself.
- A gas is produced in the reaction without heating.
- A solid is produced in the reaction without cooling.
What happens in a chemical reaction?
Some bonds are broken and others form to make new chemicals.
What does not happen in a physical change?
No bonds are broken or formed.
When balancing a chemical reaction, what must we not change?
The chemical formulae i.e. the ‘small’ numbers cannot change.
What do we mean by a balanced chemical reaction?
There are the same number of atoms of each element in the reactants and in the products.
e.g. if there are 2 oxygen atoms in the reactants, there must be 2 in the products.
What is wrong with this balanced equation? 2Ca + O2 = 2CaO
An = symbol is used instead of an arrow (the 2 in O2 should also be a subscript).
How do you identify an exothermic reaction?
An increase in temperature as energy is transferred to the thermal store of the surroundings.
How do you identify an endothermic reaction?
A decrease in temperature as energy is transferred from the thermal store of the surroundings.
What is oxidation?
When an element combines with oxygen to form a compound.
What is combustion?
When a fuel rapidly reacts with oxygen transferring energy to the thermal store of the surroundings (high temperature).
Rusting would be an example of what type of chemical reaction?
Oxidation.
Are metal oxides acidic or alkaline?
Alkaline.
e.g. sodium hydroxide is a drain cleaner.
Are non-metal oxides acidic or alkaline?
Acidic.
What happens when a compound combusts?
Each element in the compound forms an oxide.
Methane is a hydrocarbon (it contains carbon and hydrogen), what products form when it combusts?
Water (oxidation of hydrogen) and carbon dioxide (oxidation of carbon).
What is thermal decomposition?
A compound is broken down by heat.
What is a test for carbon dioxide?
Bubble through limewater (the limewater turns cloudy).
What happens in displacement?
A more reactive metal takes the place of a less reactive metal in a compound.
Why are alkali metals (group 1 elements) reactive?
They have 1 electron in their outer shell.
Why are halogens (group 7 elements) reactive?
They have 7 electrons in their outer shell.
Why are noble gases not reactive?
They have a full outer shell.
If a less reactive metal is added to a salt solution containing a more reactive metal, what will happen?
Nothing (no reaction will occur).
What do all acids have in common?
They contain hydrogen.
An acid releases what into solution?
Hydrogen ions (positive).
