Chemical Reactions Flashcards
What happens in a chemical reaction?
Some bonds are broken and others form to make new chemicals.
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 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 oxidation?
When an element combines with oxygen.
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.
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.
What do all acids have in common?
They contain hydrogen.
An acid releases what into solution?
Hydrogen ions (positive).
An alkali releases what into solution?
Hydroxide ions (negative).
What is neutralisation?
The hydrogen ions from an acid combine with the hydroxide ions from the alkali to form water.
Acid + alkali -> what are the products?
Salt + water.
Acid + Metal carbonate -> what are the products?
Salt + water + carbon dioxide.
What is a salt?
Hydrogen ions in an acid have been replaced by a metal.
What is thermal decomposition?
A compound is broken down by heat.
What is a catalyst?
A chemical that speeds up a chemical reaction without being used up in the reaction.
Where on the periodic table are many catalysts found?
Transition metals.
True/ False - all combustion reactions are oxidation reactions.
TRUE.
Give 3 examples of diatomic elements (they hang around in pairs)
Oxygen, Nitrogen, Hydrogen, any halogen (group 7 element)
What is wrong with this balanced equation?
2Ca+O2=2CaO
an arrow should be used instead of = and the 2 in O2 should be subscript (looks like 0₂)
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 form the surroundings
If a less reactive metal is added to a salt solution containing a more reactive metal, what happens?
Nothing (no reaction will occur)
pH 0 is a strong…
Acid
pH 14 is a strong…
Alkali
Give an example of a biological catalyst
Enzyme (lipase, amylase, carbohydrase, protease)
Catalysts _______ the _______ barrier which _______ the rate of reaction
Catalysts REDUCE the ENERGY barrier which INCREASES the rate of reaction
