2I Chemical Reactions
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What is a physical change?
No new substance is made, it is reversible. It can be a change of state, e.g. solid melting to become a liquid.
What are the four signs of a chemical reaction?
A colour change. An energy change - usually temperature Effervescence - bubbles of gas given off. Precipitation - a solid formed when two liquids are mixed.
What is the difference in substances between a chemical and a physical chage.
In a physical change the substances are the same at the end. In a chemical change the substances re-arranged and different from the start of the reaction.
When metals react with oxygen they make metal oxides. What is the general equation for this?
metal + oxygen —–> metal oxide
What is the equation for aluminium reacting with oxygen?
aluminium + oxygen ——-> aluminium oxide
Non-metal elements can also react with oxygen to make non-metal oxides. What is the equation for carbon reacting with oxygen?
carbon + oxygen —-> carbon dioxide
In carbon monoxide what does the prefix mono mean?
One oxygen
What are the prefixes for two and three oxygens?
Di = two Tri = three
What are the prefixes for four and five oxygens?
Tetr = four Pent = five
Combustion is a chemical reaction. What three things are needed for combustion to happen?
Fuel, oxygen and heat
What happens when you remove one of the sides of the fire triangle?
The fire will go out/burning will stop
How could you remove oxygen from a fire?
Fire blanket, carbon dioxide extinguisher
How could you remove fuel from a fire?
Have firebreaks between trees in a forest (you can’t really remove the fuel)
How could you remove heat from a fire?
Water
Many fuels are hydrocarbons, what are they made from?
Hydrogen and carbon
What do decomposition reactions need to break the bonds between atoms?
energy
What is the general equation for a hydrocarbon burning?
Hydrocarbon + oxygen —> carbon dioxide + water
What three types of energy can be used for decomposition reactions?
Light, electricity and heat
What is a precipitation reaction?
When an insoluble solid forms from mixing two liquid solutions.
What is the insoluble solid formed in a precipitation reaction called?
The precipitate