C3.1 Introducing Chemical Reactions Flashcards
How do you write formulae of metal elements
Written as empirical formulae
As metals exist as giant metallic lattices
How do you write the formulae of non-metal elements
Individual atoms
Weak intermolecular forces
Group 7 is diatomic molecules, attracted with weak intermolecular forces - 2 atoms covalently bonded together
Other non metal molecules exist as giant covalent structures such as carbon and silicon.
How do you write the formulae for ionic compounds
Total number of positive charges = total number of negative charges
Examples:
NaCl: 1 Na+ ion and 1 Cl- ion
With compound ions if there are more than 1 of that compound, you put it in brackets:
NaOH
Mg(OH)2
Law of conservation of mass
Same atoms are present at the start and end of a reaction
Just joined in a different way
Total mass stays the same during a chemical reaction
Why the mass seems to change during some reactions
Substances can leave or enter the reaction mixture in a non-enclosed system
Usually happens in an open container when the reaction involves a substance in the gas state
What are balanced equations and word equations
Word equations:
Simple model for a chemical reaction
Shows the names of reactants and products involved
Balanced equation: more detailed model
Shows how the atoms are rearranged in a reaction
Relative amounts of each substance involved
Need to consider ion charges from each periodic table group and diatomic elements
How do you write balanced equations
Balanced when there are equal numbers of atoms of each element on both sides of the arrow
Step 1: Write the word equation and write formula for each substance under
Step 2: Add numbers on the left of 1 or more formulae, if necessary, making equal numbers of atoms on each side
Need to consider ion charges from each periodic table group and diatomic elements
Use CHOMO (hint: not a FNAF character)
What are state symbols
Show the physical state of each substance in a chemical reaction
Written in subscript letters in brackets next to products/reactants
State symbol-meaning
(s) - solid
(I) - liquid
(g) - gas
(aq) - aqueous solution
What are half equations
Model for the change that happens to 1 reactant in a chemical reaction
Balance charges
Balance numbers of atoms
Make sure of diatomic elements (H, N, F, O, I, Cl, Br)
Example: 2Na(s) + Cl2(g) -> 2NaCl(s)
Atom to ion example: Cl2 + 2e- —> 2Cl- (reduction)
Ion to atom example: Cl2 —> 2Cl- + 2e- (oxidisation)
What are ionic equations
Show the ions present in a reaction mixture
Also includes the formulae of any molecular substances present
Example:
Default: HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)
Ionic equation: H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) - Na+(aq) + Cl-(aq) + H2O(l)
H2O is not split up as it is covalently bonded not ionic bonding.
What are spectator ions
Ions that appear in the same form on both sides of the equation.
They are in the reaction mixture but do not take part in the reaction
Net ionic equation
Leaves out spectator ions
Form an ionic equation using half equations (links to C3.4 Electrolysis)
- Write down the anode half equation: 2Cl- —> Cl2 + 2e-
- Write down the cathode half equation: 2H+ + 2e- —> H2
- Combine both equations, keeping same species on either side of arrow: 2Cl- + 2H+ + 2e- —> Cl2 + 2e- + H2
- Cancel out electrons on either side: 2Cl- + 2H+ —> Cl2 + H2 (2e- goes from either side)
What is a precipitate
Product when 2 solutions are mixed
Always in solid state
What is a mole
Unit for amount of substance
1 mole of anything contains the same number of things
