Topic 1: Stoichiometry Flashcards
What is a molecule?
Two or more atoms connected by chemical bonds, which form the smallest unit of a substance that retains the composition and properties of that substance
What is an ion?
An atom or molecule where the total number of protons is not equal to the total number of electrons.
What are the characteristics of matter?
- made up of particles: atoms, molecules or ions
- particles are in constant motion
- occupies a volume in space
- has a mass
For solids, liquids and gases, outline:
- fixed volume?
- fixed shape?
- compressible?
- strength of forces between particles?
- yes, yes, no
- yes, no, no
- no, no, yes
- strong, weak, (almost) none
What does the vibration and movement of particles depend on?
Temperature
The average kinetic energy increases as the ___________ increases.
Temperature
What are the SI units for temperature?
Kelvin (K)
What is meant by absolute zero (and what is its value)?
The temperature at which all movement of particles stops (-273°C or 0K)
How do you convert temperature (°C) into temperature (K)?
Temperature (K) = Temperature (°C) + 273
How is a change in state caused?
When the temperature increases/decreases, the average kinetic energy of the particles does the same, resulting in a change in state
Which changes of state are exothermic?
Condensing and freezing as energy is transferred to environment
Which changes of state are endothermic?
Melting and boiling as energy is transferred from environment
Does the temperature change whilst changing state?
There is no change in temperature when changing state as the energy is used to break/form bonds
What is the change of state for solid to:
- liquid
- gas
- melting
- sublimation
What is the change of state for liquid to:
- solid
- gas
- freezing
- boiling
What is the change of state for gas to:
- solid
- liquid
- deposition
- condensing
What is matter?
Any substance that occupies space and has a mass
What is a mixture?
A combination of two or more pure substances that retain their individual properties
What is a pure substance?
A substance with a definite and constant composition
What is an element?
A substance made up of atoms that each have the same atomic number
What is a compound?
A substance made up of a combination of atoms or ions chemically bonded together
What is a homogeneous mixture?
A mixture that has both uniform composition and properties throughout
What is a heterogeneous mixture?
A mixture that has non-uniform composition and varying properties
What is an anion?
A negatively charged ion
What is a cation?
A positively charged ion
What is atomic mass?
The mass of a single atom
What is a chemical reaction?
A reaction in which bonds in the reactants are broken and bonds in the products are formed and vice versa resulting in an energy change between the reacting system and its surroundings
What is concentration?
A measure of the amount of substance dissolved per unit of volume
What does it mean if a reactant is in excess?
There is more of it than needed to react with all of the limiting reagent
What is the empirical formula?
The simplest whole number ratio of atoms of each element present in a compound
What is the relative formula mass (Ar)?
A weighted average of the atomic masses of the isotopes and their relative abundances of an element
What does the structural formula show?
Visually shows the arrangement of atoms and bonds within a molecule
What is a limiting reagent?
The reactant which is used in its entirety and will determine the theoretical maximum amount of product formed
What is a mole?
The amount of substance that contains a number of specified species equal to Avogadro’s constant (6.022 x 10^23)
What is a solute?
A substance that is dissolved into another (the solvent)
What is a solvent?
A substance that dissolves another (the solute)
What is percentage yield?
The experimental yield as a percentage of the maximum theoretical yield, determines the efficiency
What is the yield?
The amount of product
What are the state symbols for:
- solid
- liquid
- gas
- aqueous
- (s)
- (l)
- (g)
- (aq)
What is atom economy?
The amount of starting materials that become useful products
Do you want a high or a low atom economy?
A high atom economy as it means that less waste is created and the reaction has a high efficiency
How do you calculate the atom economy?
Atom economy = (molecular mass of atoms of useful products / molecular mass of atoms in reactants) * 100
What is the molar mass?
Mass of 1 mole of a substance (g mol-1)
How do you convert from moles to mass?
m = Mr * n
How do you convert from moles to number of particles?
Number of particles = n * Avogadro’s constant
What is an isotope?
Atoms with the same number of protons and a different number of neutrons
What is the relative abundance of an isotope?
A measure of the percentage of isotopes present in an element
What is the relative molecular mass (Mr)?
Combination of individual Ar values of atoms in a molecule
What is the molecular structure?
The actual number of atoms of each element present in one mole of a compound
What is stoichiometry?
The quantitative method of examining the relative amounts of reactants and products
What are some common factors that decrease the percentage yield?
- loss of products from reaction vessels
- impurity of reactants
- changes in reaction conditions, such as temperature and pressure
- reverse reactions consuming products in equilibrium systems
- existence of side reactions due to impurities
What can be said about the pressure and temperature of an ideal gas?
- high temperature
- low pressure
What is the Standard Temperature and Pressure (STP)
- 273K
- 100kPa
What is the molar volume of an ideal gas at STP?
22.7dm^3/mol
What is Avogadro’s Law?
Equal volumes of any gas measured at the same temperature and pressure contain the same number of molecules
When can Avogadro’s Law be applied?
In stoichiometric relationships in which the coefficients correspond to the ratio of volumes of gases
What is the equation for Avogadro’s Law?
V1 / n1 = V2 / n2
What is Boyle’s Law?
V1p1 = V2p2
What is Charles’ Law?
V1 / T1 = V2 / P2
What is Gay-Lussac’s Law?
p1 / T1 = p2 / T2
What is the combined Gas Law?
p1V1 / T1 = p2V2 / T2
What is the ideal gas equation?
pV = nRT
How do you calculate the number of moles from concentration and volume
n = CV
What is a titration?
A chemical reaction where a standard solution of known concentration is added to a solution of unknown concentration until the reaction is complete
