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
