Chemical Reactions Flashcards
What are chemical reactions?
Chemical reactions are how new substances are made between elements and compounds.
They can be complicated industrial processes or simple everyday actions e.g. Cooking food or burning fuels
What are the ways in which chemical changes are different from physical changes?
In a chemical change new substances are formed
In a physical change the substances stay the same they just exist in a different form
Chemical changes are very hard, sometimes impossible to reverse you can’t un-bake a cake or un-burn a lump of coal
Physical changes of state are quite easy to reverse you can melt ice or condense steam to get the water back
What do chemical reactions always need?
Energy change
It can be endothermic or exothermic reactions
What is an endothermic reaction?
An endothermic reaction requires energy to make it happen
What is an exothermic reaction?
An exothermic reaction e.g burning fuel releases energy and does not need energy introduced to make it happen
What is oxidation?
Oxidation is the name given to the reaction between another substance and oxygen e.g. Magnesium + oxygen = Magnesium Oxide
Give two examples of oxidation?
When iron rusts we see formation of Iron Oxide
When a bite is taken from an apple the inside will go brown
What is combustion?
The reaction that happens when any substance burns in oxygen eg burning fossil fuels,- give out a lot of heat
Not all oxidation is combustion but burning always needs oxygen
What are the 3 sides of the fire triangle?
Fuel
Oxygen
Heat
When something burns in air it is the oxygen present in the air that is used in the reaction
What is a chemical equation?
Short hand ways of describing chemical reactions
Either as word or symbols and formulae
Eg magnesium plus oxygen goes to magnesium oxides
2Mg + 02->2MgO
This is because oxygen molecules have 2 atoms and magnesium atoms exist alone so 2 magnesium atoms are needed for each oxygen atom
Salt : 2Na + Cl2 ->2NaCl
What is photosynthesis as equation?
Water + carbon dioxide in the presence of chlorophyll and sunlight -> glucose + oxygen
Reactants on left and products on right
Things present are written above and below
Examples of chemical reactions - salt
Sodium chloride = white solid = salt
Comes from sodium = soft grey metal = dangerous
And chlorine = green gas = poison or disinfectant
Example of chemical reaction - sugar
Sugar = white sweet solid comes from Carbon = black solid reacts with Oxygen = colourless gas Hydrogen = colourless gas highly reactive
