Chemical Reactions/Physical Changes Flashcards
What is a chemical reaction
Something that can’t be reversed
Something that creates one or more new chemical substances
Signs of a chemical reaction
A change in temperature Light energy being given out A change in mass as a gas escapes Bubble that show us a gas is being made A change in colour A smell given out
What is a physical change
Something that can be reversed
Something that does not create a new chemical substance (product)
Always the same substance
Signs of a physical change
Change in state (solid, liquid, gas)
Change in temperature, shape, texture, colour
Examples of a chemical reactions
Anything that includes cooking, rusting, sticking, burning, making metals. Frying an egg Baking a cake Lighting a match Burning petrol Making alcohol from sugar and yeast Neutralising an acid
Examples of a physical change
Anything that includes melting, freezing, condensing and evaporating Making toast Boiling in a kettle Melting iron alcohol evaporating Freezing yogurt melting ice
How to test for hydrogen
Equation?
Place a burning splint next to the mouth of a test tube that contains a metal and an acid.
A ‘squeaky look as the gas ignited, shows that hydrogen has been produced
Metal (magnesium)+acid->water+hydrogen
How to test for carbon dioxide
Equation?
Put an acid and a metal carbonate into a test tube. Then put a delivery tube on it. Get limewater and pass some of the liquid into the lime water through the tube.
When carbon dioxide gas is bubble through the lime water it turns it cloudy or milky white.
Metal carbonate (calcium carbonate)+ acid -> salt+water+carbon dioxide
How to test for oxygen
Place a glowing/freshly extinguished splint next to the mouth of a test tube that contains a sample of gas.
If the splint relights, this shows that oxygen is present.
Combustion
The scientific word for burning is combustion. This is burning of a substance to realise energy
When burning takes place, a chemical reaction always happens. The substance that burns reacts with the chemical in the air called oxygen and makes a new chemical called an oxide or a dioxide. If a fire can’t get any oxygen it goes out.
Fire triangle
The fire triangle tells us that three things are needed in order for fuel to burn-oxygen, fuel and heat. A burning candle uses up oxygen in the air. The air is made up of 16% of this gas.
To put out a fire you have to take at least one side of the triangle away.
Examples of fuels
paper, oil, woods, gases, fabrics, liquid, plastics, and rubbers
Reactants and products
The starting substances used in a reaction of reactants. New substances formed in the reaction are products.
What does the arrow mean
It means ‘change into’.
In a chemical reaction, all the reactants change into products. It is difficult to reverse a chemical reaction and change products back into reactants.
How is combustion used in everyday life?
To keep warm, cooking, starting fires
