DEFINITIONS Flashcards
Give the meaning of the term electronegativity.
Power of an atom to attract a pair of electrons in a covalent bond.
State the meaning of the term periodicity
Repeating pattern/trends (of physical or chemical properties/reactions)
Explain what is meant by the term stereoisomers.
:compounds with the same structural formula but different arrangement of atoms in space
Define the mass number of an atom.
Number of protons + neutrons
State the meaning of the term atomic number
The atomic number (i.e. proton number), Z is equal to the number of protons.
State the meaning of the term isotope
Isotopes are atoms with the same number of protons but a different
number of neutrons.
State the meaning of the term ionisation
amount of energy needed to remove a mole of electrons from a mole of atoms, in the gaseous state.
State the meaning of the term Relative Atomic Mass - Ar
Relative Atomic Mass (Ar) = Average mass of one atom of an element / 1/12th the mass of a C12 atom
State the meaning of the term Relative Molecular Mass - Mr
Relative Molecular Mass (Mr) = Average mass of one molecule compared to 1/12th the mass of a C12 atom
State the meaning of the term Empirical formula
simplest whole number ratio of atoms of each element.
State the meaning of the term Molecular Formulae
the actual number of atoms of each element.
Definition of The Avogadro Constant
The Avogadro Constant is the number of atoms in 12g of C12
Definition of a Nucleophile
• An electron-pair donor
What is a positive inductive effect?
The ability to release electron density through a covalent bond
Definition of Structural Isomerism
Structural isomers have the same molecular formula but different structural formula.
What is mass spectrometry
A machine that can be used to analyse elements or compounds, it accurately determines atomic mass or relative molecular mass
Define percentage yield
The percentage of product produced by a reaction compared to a theoretical maximum
Definition of reducing agent
(Remember is itself oxidised so OIL)
Electron donor (giving away e-)
Define the term standard enthalpy of combustion. (3)
The enthalpy change when
1 mol of a compound is burned in oxygen completely substances in standard /
specified states
State what is meant by the term hydration.
splitting of a molecule by the addition of water
State what is meant by the term mean bond enthalpy.
Energy required) to break a given covalent bond of gaseous molecules into gaseous atoms (1) averaged over a range of compounds (1)
define Exothermic Processes
Energy is released from the chemical to the surroundings during the process
The temperature of the surroundings increases
define Endothermic Processes
Energy is taken in by the chemical from the surroundings during the process
The temperature of the surroundings decreases
define Enthalpy Changes, ΔH
the change in heat energy at constant pressure
define Activation Energy, Ea
Ea, is the minimum needed energy to start a reaction.
define the standard enthalpy of combustion
· The enthalpy change when one mole of a substance
· is completely burnt in excess oxygen
· all reactants and products being in their standard states
Question: Why may the enthalpy of combustion of a compound be difficult to measure?
Incomplete combustion may occur
define Hess’ Law
enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products.
Assumption made in calorimetry:
The energy transferred to the water from the reacting chemicals (or vice versa for endothermic reactions) is equal to the energy released (or taken in) by the reaction.
Sources of Error in calorimetre
Heat loss to the surroundings
· Incomplete combustion of the fuel
· Heat energy transferred to the metal calorimeter
· Some fuel evaporates
Improvements to Minimise Sources of Error
solution/solid:Add a lid – reduces heat loss
· Insulate sides of calorimeter using poylsterene – reduces heat loss
comb: Reduce distance between flame and beaker – reduces heat loss
· Put sleeve around flame to protect it from draughts
Steps to Measure an Enthalpy Change Using a Cooling Curve
Record the temperature for a suitable time (3 minutes) before adding reactants together
· To establish an accurate initial temperature
· Mix reactants then record temperature every minute until a trend is seen
· Plot a graph of temperature against time
· Extrapolate the cooling curve back to the point of addition
· To establish a theoretical temperature change accounting for heat loss
define Reducing agent
Electron donor
define Oxidising agent
Electron acceptor
define Redox reaction
Reaction involving the oxidation of one species and the reduction of another
Definition of homogenious system
A homogenious system is one where all reactants and products are in the same phase.
define Acid
Proton Donor
define Base
Proton Acceptor
define pH
pH = -Log10[H+]
define [H+]
[H+] = 10-pH
How to get pKa from Ka =
= -Log10Ka
How to get Ka from pKa
= 10-pKa
Kw =
[H+][-OH]
Define molecular formula.
A formula that tells us the actual number of atoms of each different element that makes up a molecule.
Mean bond enthalpies are always endothermic processes and have a
positive sign.
This is because energy is required to break bonds. what does a positive value indicate about strength of bond
The more positive the
bond enthalpy the larger the amount of energy needed to break the bond and so the stronger
the bond.
a)State why the enthalpy of formation of Na(s) is zero.
b) State why the enthalpy of formation of liquid Na is not zero.
a) Na is an element
b) Na(l) is not the standard state of Na (so doesn’t have to equally 0 as in definition specifically has to be in standard condition which na is solid in sc)
mean bond enthaply;
Give one reason why the bond enthalpy that you calculated above is
different from the mean bond enthalpy quoted in a data book.
why theoretical are different than experimental values
The data book value is averaged over a range of different compounds (not just
CH3CHF2 molecules).
In a real reaction the values are not mean values! Also watch out for changes of state as mean bond enthalpies
are for gases.
