Unit 2: Chemistry In Action Flashcards
Define endothermic
Give an example
A reaction in which heat is taken in as the reactants change to products
This the temperature drops
Breakdown if limestone (CaCO3) to lime (CaO) and carbon dioxide
Or heating blue copper sulphate to break into anhydrous copper sulphate and water
Define exothermic
Give an example
A reaction in which heat is given out as the reactants change to products
Thus the temperature rises
E.g. Neutralising an acid with an alkali
Or anhydrous copper sulphate and water to give blue copper sulphate
Define enthalpy change
A measure of heat change in which energy is taken in or given out when a chemical or physical change occurs at a constant pressure
What is thermochemistry
The study of heat changes during chemical reactions
What must happen for bonds to be broken and formed
Energy must be put in to break bonds
Energy must be given out when bonds are formed
So most chemical reactions involve an energy change
If a reaction is endothermic in one direction what will it be in reverse?
Exothermic
What are the standard conditions for measuring enthalpy changes
100kPa pressure (approx normal atmospheric pressure) 298K temperature
What is the standard state of an element
The state in which it exists at 298K and 100KPA
What does a negative enthalpy change indicate?
The reaction is exothermic as it has lost energy to the surroundings
Standard molar enthalpy of formation definition
The enthalpy change when one mole of substance is formed from it constituent elements under standard conditions and when all reactants and products are in their standard states
Standard molar enthalpy of combustion definition
The enthalpy change when one mole of substance is completely burned in oxygen under standard conditions and when all reactants and products are in their standard states
How can we measure heat change?
To measure the enthalpy change we arrange for heat to be transferred into a particular mass of a substance, often water
Q=mass x specific heat capacity x temp change
What is a calorimeter
An instrument for measuring get changers that accompany chemical reactions
What is the flame calorimeter?
An improved version of ten simple calorimeters used for measuring enthalpy changes of combustion
It incorporates the following to reduce heat loss: spiral chimney made of copper, enclosed flame, fuel burns in our oxygen rather than air
Why can the hydrolysis of a haloalkane by sodium hydroxide solution not be carries our in water?
Haloalkanes do not mix with Waite do ethanol is used as a solvent in which the haloalkane and the aqueous sodium hydroxide both mix
This called a hydrolysis reaction
State reactivity trend of Haloalkanes
Less reactive as we go down the halogen group
Because C-X bond gets stronger
Boiling point trends haloalkanes
Increases with increased chain length
Increases as we down the halogen group
Because more van der waals forces due to larger molecules and more electrons
Define nucleophile
An ion/group of atoms with a negatively charged area/partially negative charged area that takes part in an organic reaction by attacking an electron deficient area in another reactant
Has a lone pair of electrons which it can use to form a covalent bond
What is nucleophilic substitution
An organic reaction in which a molecule with a partially positive charged carbon atom is attacked by a reagent with a negative charge (a nucleophile)
It results in the replacements of one of the groups or atoms on the original molecule by the nucleophile
What is the leaving group?
In organic substitution reaction, the leaving group is an atom that is ejected from the starting material, normally taking with it an electron pair forming a negative ion
(Halide ion)
Name 3 common nucleophile a
Hydroxide ion -:OH
Ammonia :NH3
Cyanide ion -:CN
In elimination reactions, what acts as a base?
OH- group
Removes H+ ion from the haloalkane
What is a CFC
Chlorofluorocarbons are haloalkanes containing both chlorine and fluorine atoms but not hydrogen
E.g. CCL3F , CCl2F2 etc.
General formula of haloalkane
CnH2n+2X shortened to R-X
