Formulae and equations Flashcards
Key concepts in chemistry
aqueous
Definition
Dissolved in water to form a solution. Shown as (aq) in chemical equations.
atom
Definition
The smallest part of an element that can exist.
balanced chemical equation
Definition
A chemical equation written using the symbols and formulae of the reactants and products, so that the number of units of each element present is the same on both sides of the arrow.
charge
Definition
Electrical charge can be positive or negative. Like charges (+ and + or - and -) repel but unlike charges (+ and -) attract each other.
compound
Definition
A substance formed by the chemical union of two or more elements.
covalent bond
Definition
A bond between atoms formed when atoms share electrons to achieve a full outer shell of electrons.
covalent compound
Definition
Compounds, commonly formed between non-metal elements, by sharing electrons between atoms to form covalent bonds. All molecular compounds are covalent.
electron
Definition
Subatomic particle, with a negative charge and a negligible mass relative to protons and neutrons.
element
Definition
A substance made of one type of atom only.
formula
Definition
A combination of symbols that indicates the chemical composition of a substance.
insoluble
Definition
Unable to dissolve in a particular solvent. For example, sand is insoluble in water.
ion
Definition
Electrically charged particle, formed when an atom or molecule gains or loses electrons.
ionic bonding
Definition
Ionic bonding forms between two atoms when an electron is transferred from one atom to the other, forming a positive-negative ion pair.
ionic compound
Definition
An ionic compound occurs when a negative ion (an atom that has gained an electron) joins with a positive ion (an atom that has lost an electron).
ionic equation
Definition
A chemical equation that shows how positively charged ions join with negatively charged ions to make a compound.
metal
Definition
Shiny element that is a good conductor of electricity and heat, and which forms basic oxides.
molecule
Definition
A collection of two or more atoms held together by chemical bonds.
non-metal
Definition
Element that is a poor conductor of electricity and heat, and which forms acidic oxides.
particle
Definition
A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules.
precipitate
Definition
A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, eg in a precipitation reaction.
precipitation reaction
Definition
A reaction in which an insoluble solid is formed when certain solutions are mixed.
product
Definition
A substance formed in a chemical reaction.
reactant
Definition
A substance that reacts together with another substance to form products during a chemical reaction.
soluble
Definition
Able to dissolve in solvent. For example, sugar is soluble in water because it dissolves to form sugar solution.
spectator ion
Definition
An ion that is exactly the same on both sides of an ionic equation.
state symbol
Definition
A symbol used in chemical equations to show if a substance is a solid, a liquid, a gas, or an aqueous solution.
subscript
Definition
A letter or number written below the line.
word equation
Definition
An equation in which only the names of the reactants and products are used to model a reaction.
Each element is represented by its own chemical symbol. A chemical symbol:
- consists of one or two letters
- always starts with a capital letter, with any other letter in lower case
Chemical symbols
capitals and lower case
First letter is a capital second is lower case.
The formulae for most elements is just their symbol, but there is a group of non-metal elements that exist as molecules that contain two atoms joined together. To show this, their formulae all have a subscript number 2 in them. For example:
iodine, I(2)
bromine, Br(2)
chlorine, Cl(2)
fluorine, F(2)
oxygen, O(2)
nitrogen, N(2)
hydrogen, H(2)
there is a group of non-metal elements that exist as molecules that contain two atoms joined together. To show this, their formulae all have a subscript number 2 in them.
A mnemonic can be used to remember these elements:
IBring Clay For Our New House
A substance formed by the chemical union of two or more elements is called what?
Compound.
The chemical formula for a compound shows:
- the symbols for each element in the compound
- the number of atoms of each element in a unit of the compound
What is a bond formed between two atoms, where electrons are shared called?
A covalent bond
Covalent compounds usually form between what type of element and are held together by what?
Covalent compounds usually form between non-metal elements and are held together by covalent bonds.
All compounds that exist as molecules are what type of bond?
Covalent
Some examples of covalent compounds:
Amonia NH(3)
Carbon dioxide CO(2)
Methane CH(4)
Sulfur dioxide SO(2)
Water H(2)O
The subscript numbers in formulae show what?
The subscript numbers in formulae show how many atoms of that element appear in the molecule.
A bond formed between two atoms where an electron is transferred from one atom to the other is called what?
An ionic compound
Ionic compounds are made up of what?
Ionic compounds are made up of atoms joined together by ionic bonds.
Ionic compounds contain what type of element(s)?
They usually (but not always) contain at least one metal element and one non-metal element.
What is a charged particle formed when an atom, or a group of atoms, loses or gains an electron called?
An ion
How are the number and sign of an ion’s electrical charge(s) shown?
In subscript text
examples of some common ions
and their electrical charges
Sodium Na+
1 +
1 -
Magnesium Mg(2)+
2+
2-
Chloride Cl-
2+
2-
Oxide O(2)-
2+
2-
How can the formula of an ionic compound be predicted?
The formula of an ionic compound can be predicted by using the formulae of its ions. The numbers of ions in a formula must give an equal number of positive and negative charges.
Formula and electrical charges of sodium chloride
NaCl
1+
1-
Formula and electrical charges of sodium oxide
Na(2)O
2+
2-
Formula and electrical charges of magnesium oxide
MgO
2+
2-
Formula and electrical charges of magnesium chloride
MgCl(2)
2+
2-
What is a word equation?
A word equation models a chemical reaction using the names of the substances involved. Word equations do not show any chemical symbols or formulae.
What are the substances that react together in a chemical reaction called?
Reactants
In a chemical reaction what happens to atoms and ions in reactants?
In a chemical reaction, the atoms or ions in reactants separate from one another.
They join back together in a different way to form products.
How are products formed in a chemical reaction?
In a chemical reaction, the atoms or ions in reactants separate from one another. They join back together in a different way to form products.
Word equations always take what form?
reactants → products
In a word equations, what is the function of the + sign?
A + sign separates two or more reactants, or two or more products.
Example word equation
Potassium hydroxide reacts with sulfuric acid. Potassium sulfate and water are formed in the reaction. This means that:
the reactants are potassium hydroxide and sulfuric acid
the products are potassium sulfate and water
the word equation is: potassium hydroxide + sulfuric acid → potassium sulfate + water
Q. Nitrogen and hydrogen react together to form ammonia. Give the word equation for the reaction.
Nitrogen + hydrogen → ammonia
What does a balanced chemical equation do?
A balanced chemical equation models a chemical reaction using the formulae of the reactants and products. It shows the number of units of each substance involved.
State symbols
When are they used?
What do they show?
Balanced chemical equations include state symbols in brackets after each formula. They show the physical state of that substance.
List all the state symbols
(s) solid
(l) liquid
(g) gas
(aq) aqueous solution
What does the state symbol: (s) mean?
Solid
What does the state symbol: (l) mean?
Liquid
What does the state symbol: (g) mean?
Gas
What does the state symbol: (aq) mean?
Aqueous solution
How is an aqueous solution formed?
An aqueous solution forms when a substance dissolves in water.
What does a balanced ionic equation show?
A balanced ionic equation shows the reacting ions in a chemical reaction.
What is a balanced ionic equation used to model?
These equations can be used to model what happens in precipitation reactions.
What happens in a typical precipitation reaction?
In a typical precipitation reaction, two soluble reactants form an insoluble product and a soluble product.
Precipitation reactions
Example: silver nitrate solution reacts with sodium chloride solution. Insoluble solid silver chloride and sodium nitrate solution form:
AgNO(3)(aq) + NaCl(aq) → AgCl(s) + NaNO(3)(aq)
The Na+ ions and NO3- ions remain separate in the sodium nitrate solution and do not form a precipitate. Ions that remain essentially unchanged during a reaction are called spectator ions.This means you can ignore them when you write the ionic equation. You only need to model how the solid silver chloride forms:
Ag+(aq) + Cl-(aq) → AgCl(s)
What should stay the same on either side of the reaction in a balanced ionic equation?
The number of positive and negative charges
The number of atoms of each element
Q. Explain why this ionic equation is balanced: Ba^2+(aq) + SO(4)^2-(aq) → BaSO(4)(s)
There are the same numbers of atoms of each element on both sides of the equation. The total charge on both sides is also the same (zero).
Q. Balance this ionic equation, which models the formation of a silver carbonate precipitate: Ag+(aq) + CO(3)^2-(aq) → Ag(2)CO(3)(s)
2Ag+(aq) + CO(3)^2-(aq) → Ag(2)CO(3)(s)
Q. Balance this ionic equation, which models the formation of an aluminium hydroxide precipitate: __Al^3+(aq) + __OH-(aq) → Al(OH)(3)(s)
Al^3+(aq) + 3OH-(aq) → Al(OH)(3)(s)
What is the correct formula for ammonia?
NH(3)
What is the correct formula for sodium oxide, which is formed by joining positive sodium ions (Na+) to doubly negative oxide ions (O^2-)?
Na2O is the formula, as the positive and negative charges are balanced. 2 x single positive Na+ ions and 1 x doubly negative O2- ions, gives total charges of 2+ and 2-.
What is the word equation for a reaction where hydrogen and carbon monoxide are the products, and water and carbon are the reactants?
water + carbon → hydrogen + carbon monoxide
In this unbalanced symbol equation: Na + Cl(2)2 → NaCl what is the correct balanced equation?
2Na + Cl(2) → 2NaCl
Which ions can be missed out when writing this ionic equation?
AgNO(3)(aq) + KBr(aq) → AgBr(s) + KNO(3)(aq)
The potassium (K+) ions and nitrate (NO3-) ions can be missed out as they are unchanged by the reaction; both are dissolved in water on each sides of the equation. The silver (Ag+) ions form the solid AgBr(s).
Solubility equation
Solubility (per 100g of solvent) = (mass of solid(g) ÷ mass of water removed(g)) x 100
Rf equation
Rf = distance travelled by solute ÷ distance travelled by solvent
Number of moles formula
Number of moles = Mass in g (of element or compound) ÷ Mr (of element compound
Percentage yield equation
Percentage yield = (Actual yield(grams) ÷ Theoretical yield(grams)) x 100
Concentration of a solution formula
Concentration = Number of moles (in mol) ÷ Volume of solution (in dm^3)
Acid + Base → ?
Acid + Base → Salt + Water
Acid + Metal → ?
Acid + Metal → Salt + Hydrogen
Metal + Water → ?
Metal + Water → Metal hydroxide + Hydrogen
Heat energy transferred calculation
Heat energy transferred(j) = mass of liquid being heated(g) x Specific heat capacity(j/g/degrees centigrade) x Change in temperature of the liquid(degrees centigrade)
Enthalpy change
Equation
Enthalpy change = total energy absorbed to break bonds - Total energy released in making bonds
Rate of reaction equation
Rate of reaction = Amount of reactant used or amount of product formed ÷ time
