C3 Chemical Reactions Flashcards
Why is the formula for Bromine Br2 and not Br?
Bromine exists as a diatomic molecule
What is the meaning of the Roman Numerals in Iron(II) and Iron (III)?
The number of electrons in its outer shell
Explain why a wooden log has more mass before burning than the ashes it leaves after burning despite the Law of Conservation of Mass?
Some of the particles will have evaporated as a gas. If the reaction took place in a closed system, the mass would be the same.
Explain, in terms of particles, why iron bars increase in mass after rusting.
Rust is the reaction between Iron and Oxygen - since there are now more particles since the oxygen has bonded to the iron, the mass is higher.
Explain why an unbalanced chemical equation is not a completed chemical equation.
It does not abide to the Law of Conservation of Mass - the number of particles is not the same on both sides of the equation.
What is a half-equation?
An equation to model what happens to one reactant in a chemical equation and its electrons
What is a complete ionic equation ?
An ionic equation with all of the ions in the experiment present.
What are spectator ions?
Ions that do not take part in the reaction (i.e. that are the same on both sides of the equation)
What is a net ionic equation?
An ionic equation only showing the ions that change in the reaction (i.e. ignoring spectator ions)
What is the value of Avogrado’s Constant?
6.02x10^23
What is the mole?
The amount of any substance that has the same number of entities as there are atoms in Carbon-12
What is the mass of one mole of a substance?
Its relative formula mass/relative atomic mass/molar mass
What is the equation linking mass, moles and molar mass?
Mass (g) = moles (mol) x molar mass (g/mol)
OR
Moles (mol) = Mass (g) / molar mass (g/mol)
What is a limiting reactant?
The reactant that detemines how much product is produced.
What is a reactant that is in excess?
There are more moles of the reactant in excess than the limiting reactant, so it has no effect on how much product is produced.
How do you work out which is the limiting reactant?
Calculate the number of MOLES of each substance - NEVER use the MASS
What is the stoichiometry of an equation?
The relative amounts of each substance used.
What is an endothermic reaction?
A reaction that takes in energy from the surroundings.
What is an exothermic reaction?
A reaction that releases energy to the surroundings.