Year 11 Term 1 Flashcards
What’s an exothermic reaction
One that gives out energy to the surroundings when bonds are formed
What’s an endothermic reaction
One that takes in energy from the surroundings and breaks bonds
What happens during a chemical reaction
Bonds are broken, atoms are rearranged and then bonds are reformed
Energy in a chemical reaction
Energy never created or destroyed so total amount of energy after reaction is the same as before
How do we know if it’s an exothermic reaction
If the energy of the product is lower than the reactants then energy has been released
How do we know if it’s an endothermic reaction
If the energy of the products is higher than the reactants then the energy has been taken in
How is hydrogen gas used in hydrogen fuel cells
Supplied to as a fuel to the cathode. diffuses through graphite electrode and reacts with hydroxide ions to form water and provides electrons to an external circuit
How is oxygen gas used in hydrogen fuel cells
Supplied to anode. diffuses through graphite and reacts to form hydroxide ions, accepting ions from the external circuit
What happens if you add the two electrons together
The electrons and the hydroxide ions on either side of the half equations cancel out so left with overall charge in the hydrogen fuel cell, that is the oxidation of hydrogen (the fuel)
Advantages of hydrogen fuel cells
Don’t need to be electrically recharged
No pollutants are produced
Can be a range of sizes for different uses
Disadvantages of hydrogen fuel cells
Hydrogen is highly flammable
Hydrogen sometimes produced for the cells by non-renewable sources
Hydrogen is difficult to store
Fuel cells are also useful as a potential energy source for space craft as:
They provide water
They are very efficient
They have no moving parts
They are lightweight
Functional group
The part of the molecule responsible for reactions
The functional group of alkenes is the double bonds
Homologous series
A series of compounds that have similar properties + same general formula
Combustion of Alkenes
Burn with a smokier, yellower flame (compared to alkanes)
Incomplete combustion
releases less energy per mole in combustion than alkanes
Alkane + Bromine water =
No reaction
Alkene + Bromine water =
Turns colourless
Why does the C=C bond in alkenes makes them more reactive than alkanes
Because the C=C is electron dense
the double bond can open up and other molecules can react with the carbons, ‘add’ to the alkene
these are addition reactions
What is hydrogenation and what conditions are needed for it to occur
Adding hydrogen to unsaturated alkenes, making them saturated alkanes
60*C
Nickel catalyst
Why would we want to turn alkene into alkane
Straighten the molecules
increase melting point
e.g. to make margarine (enough hydrogen to make it spreadable from the fridge (not too solid) but not too much that it’s a liquid)
Advantages of hydrogenation
As now solid, can be used as a spread
More useful
Disadvantages of hydrogenation
Saturated fats not healthy option, as the molecules pack closely together, making it harder for body to break it down
What is hydration and what conditions are needed
It’s the addition of water, it’s reversible so ethanol can break down into steam and ethene. unreacted ethene and steam are recycled over the catalyst
Concentrated phosphoric acid catalyst
High temp and pressure
In all addition reactions…
Only one molecule of halogen, hydrogen or water is needed as only one double bond to open up
Halogens and hydrogen
One bromine from bromine molecule bonds to one carbon from the double bond, then the other Br bonds to the other carbon from the double bond
Hydrogen the same but with H-H
Water
H bonds to one of the carbons, then OH bonds to the others
How does fermentation work
Extract sugar (glucose) from crops
Add yeast to glucose (enzymes in yeast act as catalyst)
Fermentation - 30-40*C, CO2 released
Advantages of fermentation
Sugars (renewable source)
batch process is cheap so is the equiptment needed
more carbon neutral
Disadvantages of fermentation
Very slow
very impure- needs further processing which takes time and money
Batch process (stop and start) so high labour cost
How does hydration of ethene work
Extract crude oil from the ground
oil refinery - fractional distillation then cracking to get ethene
Hydration- phosphoric acid catalyst, high temp and pressure, continuous process
Advantages of hydration
Fast reaction
Pure product
95% yield
continuous (cheaper manpower)
Disadvantages of hydration
High technology equiptment needed- expensive initial cost
high energy costs for high pressure
ethene is non-renewable
What are carboxylic acids
Carboxylics are a homologous series with the functional group COOH
Molecular formula for methanoic acid
HCOOH
Molecular formula for ethanoic acid
CH3COOH
Molecular formula for propanoic acid
C2H5COOH
Molecular formula for butanoic acid
C3H7COOH
What happens when ethanoic acid dissolves in water
The pH decreases, turning the universal indicator red
What happens when ethanoic acid reacts with a metal carbonate
Salt, carbon dioxide and water produced
How is an ester bond formed
When a carboxylic acid reacts with alcohol
What are esters
Chemicals with pleasant smells. They are used in perfumes and as solvents
Ethanoic acid + ethanol
ethylethanoate + water
Are carboxylic acids strong or weak acids
Weak acids as they don’t completely ionise in when dissolved in water. Instead only some of their molecules ionise to form H+ ions
What is condensation polymerisation
Involves monomers with two functional groups reacting, joining together usually losing small molecules such as water
What are the simplest condensation polymers produced from
Two different monomers with two of the same functional groups
What do most condensation reactions form
Either an ester bond or and amide bond
What are amide bonds between
Between carboxylic acids and amines
Where are the new bonds in condensation polymerisation usually
Where the functional groups are located
Functional groups of alcohols
-OH
Functional groups of Amine
-NH2
Difference between addition polymers and condensation polymerisation
In addition, monomers form together and no other substance is formed but in condensation another small molecule, often water is given off
What is the structure of amino acids
An amine group on one end and a carboxylic acid on the other
How are proteins made
Amino acids form polymers know as polypeptides via condensation polymerisation.
One or more long chains of polypeptides are known as proteins
What are proteins used for in the body
Enzymes used as catalysts, haemoglobin transports oxygen, antibodies form part of immune system etc
What does DNA stand for
Deoxyribonucleic acid
What is DNA
Encodes genetic instructions for the development and functioning of living organisms and viruses
What is the formation of DNA
DNA molecules are two polymer chains, made from 4 different monomers called nucleotides in the form of a double helix
What are sugars
Small molecules that contain carbon, oxygen and hydrogen
What happens when sugar reacts through polymerisation
They form larger carbohydrate polymers e.g. starch which living things use to store energy, and cellulose which is found in plant walls
