Chemistry Flashcards
Physical change
A change in a substance that doesn’t change what the substance is or its chemical properties, it only changes the appearance of a substance, so no new substances are formed.
Chemical change
When a substance combines with another and a new substance is formed.
Give examples of physical changes
Changes in shape, size, and state of matter
Give examples of how physical changes can be formed
Cutting, crushing, breaking
Can all physical changes be reversed?
Some, but not all physical changes can be reversed
Give examples of chemical changes
Burning, rusting, decomposing
What happens to the reactions in chemical reactions?
In a chemical reaction, the reactants combine together to form a new substance with different properties, energy can be given out in the form of heat or light and the change cannot be reversed.
Name some chemical reactions in living things
Digestion, respiration, photosynthesis
Word equation
They show the chemicals that react and are produced in a chemical reaction
Reactants
The substances that react together
Product
The new substances that are made in the reaction
Types of chemical reactions
When the reactants combine and form a new product and when the product breaks apart to produce 2 or more new substances
Burning
A chemical reaction in which a substance reacts with oxygen gas from the air, releasing heat and often light, and producing new substances
Is burning a physical or chemical change?
Chemical change
What is the new substance formed when burning?
Sometimes ash forms as the new substance
How can we compare the properties of reactants and products?
By comparing their physical state, color and chemical composition
What are the properties of magnesium?
It is soft and shiny, malleable, conducts electricity and is an element
Melting point: 651
What are the properties of oxygen?
It is a colourless gas, element and has no smell
Melting point: -214
What is the formula for reacting with metals and acids?
Metal + acid —-> salt + hydrogen
What happens when magnesium is placed in hydrochloric acid?
They react and form magnesium chloride (a salt) and hydrogen
What happens when zinc is placed in sulfuric acid?
They react and form zinc sulfate (a salt) and hydrogen
Write the word equation for magnesium and hydrochloric acid?
Magnesium + hydrochloric acid —–> magnesium chloride + hydrogen
Write the word equation for zinc and sulfuric acid?
Zinc + sulfuric acid —–> zinc sulfate + hydrogen
How can we test for hydrogen?
By using a burning splint. If we get a squeaky pop, hydrogen has been produced
What happens when hydrogen pops?
Hydrogen + oxygen —-> water
What is the formula for reacting with carbonates and acids?
Carbonate + acid —-> salt + water + carbon dioxide
What happen when limestone is placed in hydrochloric acid?
They react and form calcium chloride + water + carbon dioxide
Write the word equation for limestone and hydrochloric acid
calcium carbonate + hydrochloric —–> calcium chloride + water + carbon dioxide
What happen when copper carbonate is placed in hydrochloric acid?
They react and form copper chloride + water + carbon dioxide
Write the word equation for copper carbonate and hydrochloric acid
copper carbonate + hydrochloric —–> copper chloride + water + carbon dioxide
How can we test for carbon dioxide?
- We can use a lighted splint
- We can use limewater, to see if it goes cloudy
What happens in a chemical reaction when they get heated?
They form new combinations so no atoms are lost and no new atoms are produced
What will happen to the mass of calcium carbonate and hydrochloric acid with a stopper?
The mass will stay the same because there is a stopper so no atoms can leave or enter
Conservation of mass
The rule that no mass is lost or gained in a chemical reaction
Who is Antoine Lavoisier?
A French scientist who carried out an experiment using the crucible in 1772. He repeated it a lot of times and found out he had an increase in mass every time so he came up with the idea that when we burn something it combines with a gas from the air that he named oxygen (He also found out that this gas is used in respiration as well)
What will happen to the mass of calcium carbonate and hydrochloric acid without a stopper?
The gas escapes into the air because the flask is open. We cant measure the mass so it appears as if the mass decreases
What will happen to the mass of magnesium and oxygen in a crucible?
The gas will increase because we are allowing oxygen to come into the crucible so the Magnesium oxide will be heavier
How can we detect chemical reactions?
- A color change
- A gas is given off
- Heat is produced
- A change in pH
- A precipitate is formed
Color change
e.g when we heat black copper oxide with sulfuric acid produces a blue solution of copper sulfate
What happens when copper oxide and sulfuric acid react together?
Copper oxide + sulfuric acid —> copper sulfate + water
Gas is given off
e.g when magnesium is placed in hydrochloric acid bubbles of hydrogen gas are given off
What happens when magnesium and hydrochloric acid react together?
Magnesium + hydrochloric —> magnesium chloride + hydrogen
Change in pH
If you add potassium to water that contains a universal indicator you see the indicator change color from green to purple. This shows that the solution has become alkaline the pH has changed
Heat is produced
e.g when potassium is placed in water, hydrogen gas is given off
What happens when potassium and water react together?
potassium + water —> potassium hydroxide + hydrogen
Neutralization reaction
A reaction in which an acid and an alkali form a salt and water and when an acid is used to neutralize an alkali, there is also a change in ph
A precipitate is formed
If you mix solutions of silver nitrate and calcium chloride, a chemical reaction takes place reaction, and an insoluble solid is formed (silver chloride). This is called a precipitate.
You might have used limewater to detect carbon dioxide.
What happens when sodium hydroxide and hydrochloric acid react together?
sodium hydroxide + hydrochloric acid —> sodium chloride + water
Why does carbon dioxide make limewater cloudy?
Carbon dioxide makes lime water turn cloudy because a precipitate of calcium carbonate forms.
What is a solution of calcium hydroxide?
Limewater
What happens when calcium hydroxide and carbon dioxide react together?
calcium hydroxide + carbon dioxde —> calcium carbonate + water
Rusting
A chemical reaction in which iron combines with oxygen in the presence of water to form iron oxide. It breaks down iron objects
Name an unuseful chemical reaction
Rusting
What is the chemical formula for rusting?
Iron + Oxygen —> iron oxide
Is rusting a chemical or physical change?
Chemical change
Rust is only formed when both ______ and _______ are present
Oxygen and water
What colour is iron oxide?
It’s an orange-brown solid
What causes iron to rust?
Water and air (or damp air)
Does iron rust if only air is available?
No, because no water is available
Does iron rust if air and water is available?
Yes, because water and air are available
Does iron rust when calcium chloride is available?
No, because calcium chloride absorbs water so the air will be dry (dry air)
Changes in all metals are _______________ but they aren’t rusting
Chemical changes
Does iron rust when water and oil are available?
No, because oil stops any air from entering
Give examples of changes in metal
Rusting and when a copper roof turns green
How can iron be protected
- It can be painted, so this stops the oxygen in the air from reaching the iron
- It can be galvanised, so this stops the oxygen in the air from reaching the iron
Galvanised
Covering iron with a layer of zinc
______ isn’t apart of the rusting reaction but it’s needed for the reaction to happen
Water
What is the word equation for iron and sulfur?
Iron + sulfur —> iron sulfide
What are the reactants for iron sulfide?
iron and sulfur
What is the product of iron and sulfur?
iron sulfide
What are the properties of magnesium oxide?
It is a white and powdery compound
Melting point: 2800
