Topic 1: Stoichiometric relationships Flashcards
What are the three states of matter? How do they differ?
Solid, Liquid, and gas
They differ in terms of the arrangement and movement of particles
What is sublimation?
from solid state directly to the gaseous state
What is deposition?
from gaseous state directly to solid state
sometimes also called desublimation, reverse sublimation
How does solid state change to a liquid state and vice versa?
solid melting to liquid
liquid freezing to solid
How does a liquid state change to a gas state and vice versa?
Liquid boiling and evaporating to gas
Gas condensing to liquid
What is the difference between energy at the solid state to the gas state?
there is more energy towards the gas state and heating provides energy and particles gain energy
there is less energy towards the solid state and cooling takes out energy so particles lose energy
What temperature can evaporation and boiling occur?
evaporation can occur at any temperature
boiling occurs at a fixed temperature
What is the difference between the 3 states: distance between particles
Solid: close together
Liquids: close but further apart than in solids
Gas: particles far apart
What is the difference between the 3 states: arrangment
Solids: regular
Liquids: random
Gas: random
What is the difference between the 3 states: shape and volume
Solids: fixed shape and volume
Liquids: no fixed shape (takes up the shape of the container) but fixed volume
Gas: No fixed volume or shape (fill the container)
What is the difference between the 3 states: movement
Solids: vibrate
Liquids: move around each other
Gas: Move around in all directions
What is the difference between the 3 states: speed of movement and energy
Solid: slowest, lowest
Liquids: faster, higher
Gas: fastest, highest
What is the difference between the 3 states: forces of attraction
Solids: strongest
Liquids: weaker
Gas: weakest
What do the particles in a solid do when heated?
They gain kinetic energy and the temperature of the solvent or solid rises
When heat energy is supplied, what is it used to partially overcome?
the forces of attraction between particles so that they can move around each other
What is an element made out of?
An element is a pure substance that contains only one type of atom
What is a compound?
A compound is a pure substance formed when two or more elements combine chemically
What is an element made out of?
An element is a pure substance that contains only one type of atom
What is an atom?
An atom is the smallest part of an element that can still be recognized as that element
What are the physical properties of sodium?
a grey, reactive metal with a low melting point
What is chlorine?
a yellowgreen poisonous gas
Are the physical and chemical properties of a compound the same as the element it’s made out of?
The physical and chemical properties of a compound are very different to those of the elements from which it is formed
What is the difference between chemical properties and physical properties?
Chemical properties dictate how something reacts in a chemical reaction
Physical properties are basically all the other properties of a substance – such as melting point, density, hardness, electrical conductivity etc.
What do elements always do when they combine to form compounds?
They always combine in fixed ratios depending on the number of atoms required
What must be represented on both sides of a chemical equation?
When a chemical reaction is represented by a chemical equation, there must be exactly the same number and type of atom on either side of the equation, representing the same number of atoms before and after this reaction
What are the four state symbols that are used to indicate the physical state of substances involved in a reaction
(s) = solid
(l) = liquid
(g) = gas
(aq) = Aqueous (dissolved in water)
What is the mixture?
A mixture contains two or more substances mixed together
What is the difference between a homogenous mixture and a heterogeneous mixture?
A homogeneous mixture has the same composition from the mixture and consist of only one phase (a solution where no individual particles can be seen and its concentration is the same throughout)
A heterogeneous mixture does not have uniform composition and consists of separate phases. They can be separated by mechanical means. (Sand in a beaker of water)
Define relative atomic mass and its symbol
The relative atomic mass (Ar) of an element is the average of the masses of the isotopes
Define relative molecular mass and its symbol
The relative molecular mass (Mr) of a compound is the some of the relative atomic masses of the individual atoms making up the molecule
What is one mole?
One mole is the amount of substance that contains the same number of particles (atoms, ions, molecules, etc.)
What value does Avogadro’s constant have?
6.02 × 10^23 mol-1
What is the molar mass (M)?
The molar mass of a substance is its Ar or Mr in grams. The units of molar mass are gmol-1.
What is the formula to figure out the number of moles, mass of substance, molar mass?
Number of moles (n) = mass of substance/ molar mass
Mass of substance = Number of moles x molar mass
Molar mass = mass of substance/number of moles
What is the formula to find mass of one molecule
Mass one molecule = molar mass/avocados constant
What is the relationship between the number of moles and the number of particles? (triangle)
How to calculate the percentage by mass of an element?
Percentage by mass of an element = (Number of atoms of the element x relative atomic mass)/relative molecular mass
What is the empirical formula?
The simplest whole number ratio of the elements present in a compound
What is the molecular formula?
The total number of atoms of each element present in a molecule of a compound (the molecular formula is a multiple of the empirical formula)
What are the three main steps in a moles calculation?
1) work out the number of moles of anything you can
2) use the chemical (stoichiometric) equation to work out the number of moles of the quantity you require
3) convert moles to the require quantity – volume, mass etc.
What is one kg and 1 tonne in grams?
1kg = 1000g
1 tonne = 1x10^6g
What does it mean when an element is in excess?
It means that there’s more than enough to react with all the other reactants.
This means we do not need to worry about the moles of that element
What formula do you use to calculate moles questions and involving mass?
m: mass
n: coefficient
M: molar mass of substance
On slide 24 of ppt
What is the theoretical yield versus the actual yield?
A theoretical yield is the maximum possible yield that can be obtained and the actual yield is the actual yield.
How to calculate % yield?
% yield = actual yield/theoretical yield x 100
What is the limiting reactant?
It is the reaction that is used up before the others. When the limiting reactant is completely used up, the reaction stops
What do you need to know to do a moles question? What happens if you are given the masses of more than one reactant?
To do a moles question you need to know the mass of just one of the reactants. If you are given the masses of more than one reactant, you must consider that one of these reactants will be the limiting reactant and you must use this one for all calculations.
What is ideal gas?
The concept invented by scientist to approximate the behavior of real gases
When do gas deviate the most from ideal?
Gas deviate most from ideal behavior at high pressure and low temperature
1 cm3 = ___ml
1ml
What is avogadro’s law on volumes of gases?
equal volumes of ideal gaes measured at the same temperature and pressure contain the same number of molecules
What does STP stand for?
Standard temperature and pressure = 273K, 100kPA (1 bar)
100kPa= _____ Pa
100kPa = 1.00x10⁵Pa
What is molar volume? What is the molar volume of an ideal gas at STP?
The volume occupied by one mole of gas under certain conditions
22.7 dm3 mol-1 or 2.27x10-2m3mol-1
What is the relationship between the number of moles of a gas and its volume?
How to convert ˚C to K?
Add 273
How to convert between cm³ and dm³
divide or times by 1000
dm³ is smaller
What is Boyles law? What is the formula?
A constant temperature, the volume of a fixed mass of an ideal gas is inversely proportional to its pressure
P= k/V or PV=k
What is the relationship between pressure and volume of a fixed mass of ani ideal gas at constant temperature? (graph)
What does the graph of pressure against 1/volume look like?
Would be a straight line graph
Why does the graph of pressure against 1/volume never actually pass through the origin?
Because the gas would have to have infinite volume at 0 perssure
What does a graph of PV against pressure (or volume) look like?
A straiht, horizontal line because PV=k, where k is a constant
What is the relationship between volume and temperature (Charles’ law)? What is an example?
The volume of a fixed mass of an ideal gas at constant pressure is directly proportional to its kelvin temperature
Therefore, if the kelvin temperature is doubled and the pressure remains constant, the volume of the gas is doubled, and vice versa.
For example: if an ideal gas has a volume of 200 cm³ at 120K, it will have a volume of 400cm³ at 240K if the pressure remains constant.
This relationship does not work for temperatures in Celsius. For instance, if the volume of an ideal gas at 25C it’s 500cm³, the volume it will occupy at 50C Will be about 560cm³.
What is the relationship between the volume and temperature (in kelvin) of a fixed mass of an ideal gas at constant pressure? (graph)
Can an ideal gas ever liquefy and why?
an ideal gas can never liquefy because there are no forces between the molecules
What is the relationship between the volume and temperature (in˚C) of a fixed mass of an ideal gas at constant pressure? (graph)
this is a linear relationship but not a proportional onebecause the graph does not pass through the origin
What is the relationshipbetween pressure and temperature?
For a fixed mass of an ideal gas at constant volume, the pressure is directly proportional to its absollute temperature: P∝T
if the temperature (in kelvin) of a fixed volume of an ideal gas is doubled, the pressure will also double
What is the overall gas law equation?
P1V1/T1 = P2V2/T2
What is the idea gas equation of the relationships between P, V and T combined with avogadro’s law?
PV=nRT
What letter represents gas constant?
R
What is the unit that stands for the gas constant?
JK-¹mol-¹
What are the units used in PV=nRT?
Use dm³ for volume and kPa for pressure
- can avoid having to convert volumes into m³
What is 1m³ equals to in cm³?
What is a solute?
a substance that is dossolved in another substance
What is a solvent?
a substance that dissolves another substance (the solute)
What is a solution?
the substance that is formed when a solute dissolves in a solvent
What is concentration of a solution?
the amount of solute dissovled in a unit volume of solution. The volume that is usually taken is 1dm³. the amount of solute may be expressed in g or mol therefore the units of concentration are gdm-³ or moldm-³
sometimes written with the unit M which means moldm-³ but it is described as ‘molar’
thus 2M would refer to ‘2 molar solution’, a solution of concentration 2moldm-³
What is the relationship between concentration, number of moles and volume solution?
number of moles can also be swapped out with mass (g)
How do you calculate density?
Density = Mass/volume
What is molar volume of a gas?
It is the volume occupied by one mole of the gas
What is the formula for the concentration in ppm?
When discussing concentrations of various pollutant gases in the air, what is the equation for concentration in ppm?
What is titration?
It’s a technique for finding the volume of solutions that react exactly with each other. One solution is added from a burette to the other solution in a conical flask. An indicator is often required to determine the end point of the titration.
What is a standard solution?
one of the solutions it reacts with to determine the concentration of a particular solution
What is water of crystallization? How can it be removed? It’s not always the case?
When substances crystallize with water.
formation of crytals using water
What substances are described as anhydrous?
substances that have lost their water of crystallisation
What can hydrated copper sulfate be obtained as?
large blue crystals
What can anhydrous copper sulfate be obtained as?
white and powdery
How can the water be removed to produce what?
by heating
When this is heated what is formed?
magnesium oxide
What is back titration?
A technique by which a note excess of a particular reagent, A, is added to another substance, X so that they react. Then the excess A is titrated against another reagent to work out how much A reacted with the substance - and therefore how many moles of X were present. This is useful when X is an impure substance
What are linked reactoins?
when the product of one reaction becomes the reactant in a second reaction
common example is the determination of the concentration of copper ions. insolution using sodium thiosulfate
