Chemistry Year 1 Definitions

Relative mass of electron

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Isotopes

Atoms of the same element of the same atomic number but different mass number (different number of neutrons). Have same chemical reactions but slight variations in physical properties

Relative Isotopic Mass

Mass of an isotope relative to one-twelfth the mass of an atom of carbon 12

Relative Atomic Mass

The weighted mean mass of an element relative to one-twelfth the mass of an atom of carbon-12.

RAM equation

[ (mass₁ x %) + (mass₂ x %0 +…] / total abundance%

Abundance of Br isotopes

79 - 49% ; 81 - 51% ; 1:1 ratio.

Abundance of Cl isotopes

35 - 75%; 37 - 25% ; 3:1 ratio

Ion

+vely or -vely charged atom or covalently bonded group of atoms where e- number is different from proton number

What is the special case of NH3 in ionic equation

it stays as is even if aq

Mole

Amount of any substance containing as many particles as there are carbon atoms in 12g of C-12

Empirical Formula

Simplest whole number ratio of atoms of each element in a compound

Molecular Formula

Actual no. of atoms of each element in a compound

Hydrated

A crystalline compound containing water molecules

Anhydrous

Substance that contains no water molecules

Water of crystallisation

Water molecules that form part of the crystalline compound - empirical formula of compound separated by dot from water of crystallisation

Methods to reduce % uncertainty

• Use larger mass as balance has fixed resolution so absolute uncertainty constant so relative %uncertainty smaller

• Heat to constant mass

• Use balance that weighs to more decimal places

Concentration equations

• conc. = mass/volume

• conc. = moles/volume

Standard Solution

Prepared by dissolving an exact mass of solute in solvent and making up solution to an exact volume

Use volumetric flask - measures volume precisely.

Molar Gas Volume

volume per mole of gas molecules at stated temp. and pressure.

At room temp. and pressure (RTP): n x 24 = V

What does volume occupied by gas depend on

• Temp.

• Pressure

• Amount of gas

Assumptions for molecules making up an ideal gas

• Random motion

• Elastic Collisions

• Negligible Size

• No intermolecular forces

Ideal Gas Equation and units

pV =nRT

• p - Pressue Pa

• V - Volume m³

• n - moles

• R - Ideal Gas Constant 8.314J/mol/K

• T - Temp. K

How to convert degrees celcius to K

+273

1 atm =

101 kPa

Theoretical Yield

Max. possible amount of product.

Why is it hard to achieve theoretical yield

• Reaction not gone to completion (e.g. reversible reaction)'

• Other side reactions may have also taken place

• Purification of product lead to loss of some product

Percentage Yield

Compared theoretical yield with actual yield.

%yield = Actual yield x 100 / theoretical yield

Atom economy

Measure of how well atoms have been utilised. 100% if only one product formed

Enthalpy

Measure of heat energy in a chemical system

Average bond enthalpy

Energy required to break one mole of a specified type of bond in a gaseous molecule. Always endothermic. If molecules not already gaseous, take into account enthalpy change for vaporisation

Activation energy

Minimum energy required to break bonds so that new bonds can form in product.

Standard condition

• temp: 298 K

• Pressure: 100kPa

• Conc.: 1mol/dm³

Enthalpy change of neutralisation

Energy change that accompanies a reaction between an acid and a base to form 1 mole of water under standard conditions with all reactants and products in their standard states

Enthalpy change of reaction

Energy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions with reactants and products in standard states

Enthalpy change of formation

Energy change that takes place when one mole of a product is formed from its elements under standard conditions with reactants and products in their standard states

Enthalpy change of combustion

Energy change that takes place when 1 mole of a substance reacts completely with oxygen under standard conditions with reactants and products in their standard states

Hess’s Law

Enthalpy change of a reaction is independent of the route taken

Rate of chemical reaction

Change on conc of reactant/products in a given time. Fastest at start.

Catalyst

Speeds up rate of reaction by providing an alternative reaction pathway of lower activation energy without getting used up.

Heterogeneous catalyst

Has different physical state from reactant. Usually solid.

Reactant molecules absorbed onto surface of catalyst and after reaction, product molecules leave surface by desorption.

Homogeneous catalyst

Same physical state as reactant.

Catalyst reacts with reactant to form an intermediate which breaks down to give product and regenerates catalyst.

Catalysis

Increases rate of industrial chemical reaction by lowering activation energy.

Lowers temp and less energy needed.

Higher atom economies = fewer pollutants.

What to always say in answer for temp and catalyst

MORE PARTICLES CAN EXCEED THE ACTIVATION ENERGY!!!

Boltzmann distribution

Graph of spread of molecular energies in gases

Changing temp, conc, adding catalyst etc changes proportion of molecules with energy higher than activation energy increases.

Molecules in gas collide with each other and container elastically - no energy lost and dont slow down

For reaction to be in equilibrium, system must be…

Closed

Position of equilibrium

Which way rate of reaction is increasingly

Le Chatelier’s Principle

When a system in equilibrium is subjected to an external change, the system will re adjust itself to minimise effect of that change.

Dynamic Equilibrium

Rate of forward reaction is equal to rate of backward reaction. Conc of reactants and products remains constant.

Pressure of gas is proportional to its

Concentration

Why do industries use compromise conditions

To give reasonable rate of reaction without shifting equilibrium position too far from desired product

If temp of a forward exothermic reversible reaction increased…

Position of equilibrium will shift to the left - towards the endothermic direction - to oppose the increase in temperature by decreasing temp of system so yield on left increases

Equilibrium constant K

Provides actual position of equilibrium. Always constant for any reaction unless temp. Changes

If Kc = 1

Position of equilibrium halfway between reactants and products

If Kc > 1

Position of equilibrium towards products

If Kc < 1

Position of equilibrium towards reactants

Homologous series

Family of compounds with similar chemical properties whose successive members differ by an addition of a CH2 group

Functional group

Part of organic molecule largely responsible for molecule’s chemical properties

Aliphatic Hydrocarbons

C-atoms joined together in unbranched/branched chains or in non-aromatic ring

Alicyclic hydrocarbons

Carbon atoms joined together in ring structure, branched or unbranched

Aromatic hydrocarbons

All or some carbon atoms found in benzene ring

General formula

Simplest algebraic formula for any member of homologous series

Displayed formula

Relative positioning of all atoms in molecule and bonds between them

Structural formula

Uses smallest amount of detail necessary to show arrangement of atoms in a molecule

Skeletal formula

Simplified organic formula

Isomers

Different compounds with same molecular formula

Stereoisomers

Compounds with same structural formula but different arrangement of atoms in space

Structural isomers

Compounds with same molecular formula, but different structural formula

Homolytic fission

Each of bonded atoms takes one of shared pair of electrons from bond

Radical

Atom or group of atoms with an unpaired electron. Extremely reactive and unstable

Nucleophile

Electron pair donor

Heterolytic fission

One of bonded atoms takes both electrons from bond and becomes negative ion (usually in polar molecules)

Curly arrows

Show movement of an electron pair when a bond is being broken or made

Sigma bond

Overlap of 2 orbital, one from each bonding atom. Is positioned on a line directly between bonding atoms. Atoms can rotate freely around the bond. Repulsion between electron pairs results in tetrahedral shape

pi bond

1 e- left in each of the 2 carbons in p orbital. Sideways overlap of p-orbital with 1e- from each carbon of double bond forms pi bond. Pi-electron density concentrated above and below line joining nuclei of bonding atoms.

Electrophillic addition

Alkenes react with electrophiles in addition reactions

Why does more alkyl groups on carbocation mean more stable carbocation

Alkyl groups donate and push electrons towards the positive charge so the positive charge is more spread out across the carbocation and makes it more stable

Polymers

Extremely large molecules formed from many repeating units of smaller molecules known monomers

Industrial polymerisation carried out at

High temp and pressure using catalyst

Feedstock recycling

Chemical and thermal processes that can reclaim monomers, gases or oil from waste polymers and used as raw materials for new polymers

Photodegradable polymers

Contains bonds weakened by absorbing light and degrade this way

Recycling

Conserves finite fossil fuels and decreases waste going to landfill.

Bioplastics

Produced from starch, cellulose, plant oils and proteins. Are renewable and sustainable alternative

Biodegradable polymers

Broken down by microorganisms into water, CO2, and biological compounds. Made from starch, cellulose etc.

Reflux

Continuous boiling and condensing of a reaction mixture.

Stops contents of flask from boiling dry or ensure contents of reaction reach certain temp without volatile chemicals evaporating

Why are anti bumping granules added

So contents boil smoothly

Distillation

Liquid with lower bpt boils first.

Vapour enters condenser and condenses and is collected in a flask

Why is water added from bottom of condenser

To ensure outer glass jacket is full

Haloalkanes

Compounds containing elements carbon, hydrogen, and at least one halogen

Hydrolysis

Chemical reaction involving water or an aqueous solution of hydroxide that causes breaking of bond in molecule.

rate of hydrolysis highest for iodoalkanes and tertiary haloalkanes

Why open end at top when heating under reflux

So no closed system otherwise pressure would build up and heat so as air expands, explodes

Distillation

Technique used to separate liquid from its impurities

Purifying organic liquids

• separating funnel used to separate liquid organic product from water

• Add aqueous sodium carbonate to mixture in conical flask. Shake to remove acid impurities.

• Acid + carbonate reaction.

• Ensure tap of separating funnel closed

• Add mixture to funnel and invert. Allow to settle

• Most dense layer at bottom (usually aqeuous)

• Add some water to identify organic layer- layer getting bigger is aqueous layer

• Place conical flask under separating funnel

• Open tap. Separate layers

• Collect organic leftover in another flask

• Add anhydrous drying agent like MgSO4 and swirl until liquid clear. Removes traces of water from organic liquid

• Filter to remove drying agent

• Do distillation. Use water bath for heating as organic liquid usually flammable

Why is there M+1 peak

Exists because 1.1% of carbon is present as the carbon 13 isotope

Types of bond vibrations

• stretching- distance between 2 atomic centres increases and decreases

• Bending- change in bond angle

• Each bond vibrates at a unique frequency

Fragmentation

Molecular ions unstable so some will break down into smaller pieces in fragmentation as fragment ions

Breaks into 2 pieces- a fragment ion and radical. Only fragment ions detected on mass spec as radicals uncharged

Amount of bond vibration depends on

Bond strength - stronger vibrate faster

Mass of each atom in bond

Each bond can absorb rad. of same frequency as natural frequency of bond vibration

Wavenumber

1/wavelength

How do greenhouse gases cause global warming

Absorb longer wavelength IR rad emitter from earth’s surface as same frequency. Vibrating bonds in molecules reemit energy as rad that increases temp of atmosphere close to earth’s surface

How is IR spectrum graph created

OR spectrometer connected to computer that plots graph of transmittance against wavenumber