OCR Unit 2 Definitions

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Atom Economy

Is a measure of how much of the products are useful

 

  Mr of desired products        x 100  *

Sum of Mr’s of all products

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(Free) Radical

Species that has an unpaired electron *

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Biofuel

Fuel derived from recently living plant material (bioethanol/biodiesel)

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Carbon Capture & Storage

The removal of waste carbon dioxide as a liquid injected deep in the oceans, as storage in deep rock formations or by reaction with metal oxides to form stable carbonate minerals.

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Percentage Yield

The mass/moles of product expressed as a percentage of what you should obtain assuming complete conversion.

 

   Actual Mass/Moles         x 100

Theoretical Mass/Moles 

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Dynamic Equilibrium

When in a closed system the rate of both the forward reaction and the backward reaction are equal.

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Le Chatlelier's Principle

The position of equilibrium will shift as to minimize the effect of any change in conditions *

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Activation Energy

Is the minimum amount of energy required for the reactants to react together *

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Rate of Reaction

The change in concentration of a reactant or product in a given time (concentration/time = moldm-3s-1)

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Catalyst

Speeds up the rate of the reaction without being used up in the process.

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Mass Spectrometry

A technique used to determine the relative isotopic masses of elements and molecules (using the molecular ion peak). It provides a useful method for identifying elements and molecules and is used in space probes and in monitoring levels of environmental pollution (eg. Lead in water supply systems)

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Infrared Spectroscopy

A technique used to identify functional groups in molecules by analysing the Infrared absorption pattern of chemical bonds. It is used in modern breathalysers and in monitoring levels of greenhouse gases in the atmosphere.

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General Formula

Simplest algebraic formula of a member of a homologous series (ie) CnH2n+2 for Alkanes (non-cyclic)

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Empirical Formula

Simplest whole number ratio of atoms present in a compound.

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Molecular Formula

Actual whole number ratio of atoms present in a compound.

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Structural Formula

The minimal detail that shows the arrangement of atoms in a molecule (ie) CH3CH2CH2CH3 for butane

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Displayed Formula

A formula that shows the relative positioning of ALL atoms and bonds within a structure.

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Skeletal Formula

A simplified organic formula, shown by removing hydrogen atoms from carbon chains, leaving just a carbon skeleton and associated functional groups.

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Hydrocarbon

A compound that contains only Carbon and Hydrogen atoms *

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Functional Group

Group of atoms in a molecule responsible for the characteristic reactions of a compound *

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Homologous Series

A series of compounds having the same functional group & general formula but with each successive member differing by CH2 *

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Structural Isomer

Molecules with the same molecular formula but with different structural formula *

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Stereoisomer

Compounds with the same structural formula but with a different arrangement of atoms in space. *

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E/Z isomerism

An example of stereoisomerism, in terms of restricted rotation about a C=C and the requirement for two different groups to be attached to each carbon atom of the C=C bond *

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Cis/Trans isomerism

A special case of E/Z isomerism in which two of the substituent groups are the same. *

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Bond fission

The breaking of a covalent bond.

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Homolytic Fission

The breaking of a covalent bond, with one of the shared pair of electrons going to each atom, forming two radicals.

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Heterolytic Fission

The breaking of a covalent bond with both of the shared pair of electrons going to one of the atoms forming ions.

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Electrophile

An electron pair acceptor

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Nucleophile

An electron pair donor *

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Saturated

A compound with no double bonds, only single carbon to carbon bonds (C-C) *

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Fractional Distillation

Separation of components in a mixture into fractions, in which each one differs in their boiling point.

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Cracking

The breaking down of long-chained saturated hydrocarbons to form a mixture shorter chained alkanes and alkenes.

 

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Free Radical Substitution

A reaction involving alkanes that involves the substitution of at least one hydrogen atom with a halogen atom via initiation, propagation and termination of radicals, themselves formed from homolytic fission.

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Unsaturated

A compound that contains at least one carbon to carbon double bond (C=C) *

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Exothermic Reaction

Reaction that releases heat energy to the surroundings.

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Endothermic Reaction

Reaction that requires the input of heat energy from the surroundings *

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Standard Conditions

Pressure of 100KPa and Temperature of 298K *

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Standard Enthalpy Change of a Reaction

Enthalpy change when the number of moles of reactants as specified in the balanced chemical equation react together in their standard states under standard conditions.

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Enthalpy Change of a Reaction

Enthalpy change when the number of moles of reactants as specified in a balanced chemical equation react together *

 

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Standard Enthalpy Change of Combustion

Enthalpy Change for the complete combustion in oxygen of 1 mole of a substance under standard conditions. All reactants and products are in their standard states 

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Enthalpy Change of Combustion

Enthalpy Change for the complete combustion of 1 mole of a substance *

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Standard Enthalpy Change of Formation

Enthalpy Change when one mole of a compound is formed from its elements under standard conditions. All the reactants and products are in their standard states *

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Enthalpy Change of Formation

Enthalpy Change when one mole of a compound is formed from its elements *

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Average Bond Enthalpy

Average enthalpy change when one mole of bonds are broken in the gaseous state. *

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Hess's Law

The enthalpy change of a reaction is independent of the pathway taken.

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Hydrolysis

Reaction with water or aqueous Sodium Hydroxide under reflux. Typically an alcohol is formed from a halogenoalkane via nucleophilic substitution.

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Dehydration

Reaction in which water is removed from an alcohol under reflux to form an alkene using concentrated sulphuric acid as a catalyst.

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