Chemical Change Flashcards
What is a physical change
It is a temporary change, the chemical composition of a substance does not change
What are the physical changes of a substance when heated
- the temperature of the substance may increase
- the substance may expand
- the substance may change colour
- the conductivity of metals decreases
- the substance may change phase
Why may a substance expand when being heated
Heating the substance increases the speed at which the particles move, since they move more energetically they occupy more volume
Why may a substance change colour when being heated
When a metal is heated it may glow red. Electrons are energised and jump to higher energy levels. When they return to the lower energy levels, they emit a form of energy which we see as light.
Why does the conductivity of a metal decrease when heated
When a metal is heated, the metal particle vibrate faster, increasing their average kinetic energy. Because of the increases particle vibration, it is more difficult for the electron too travel through the metal.
What is a chemical change
The braking or the formation of bonds. A new substance is formed
What is the name of the substances that are combined to create the new substance
Reactants
What is the name of the new substance formed in a chemical reaction
Products
Explain the synthesis of water
When hydrogen reacts with oxygen to form H2O gas, the covalent bonds in the diatomic hydrogen molecules and oxygen molecules are broken, forming hydrogen and oxygen atoms which then immediately bond to form water molecules
Explain the decomposition of water by electrolysis
When an electrical current is passed through acidified water in Hoffmann’s Voltameter, bubbles. Begin to form on the two electrode. The water is decomposed into hydrogen and oxygen.
Where is the hydrogen produced in the decomposition of water
On the negative electrode
Where is oxygen produced in the decomposition of water
On the positive electrode
What is the conservation of atoms
It states that the number of atoms remains constant during a reaction
What is the conservation of mass
It states that if the number of atoms does not change, then the total mass of the products and the reactants will be the same
What is the law of constant composition
It states that no matter how a compound is prepared, the ratio of the elements in the particular compound is fixed
