Chemistry Paper Two Flashcards
What does the rate of reaction depend on?
Temperature
Concentration of a solution/pressure of gas
Surface Area
The presence of a catalyst
Why does temperature increase the rate of reaction?
When the temperature increases, the particles all move faster. As they move faster they collide more frequently.
Why does increasing the concentration or pressure increase the rate?
The solution is more concentrated, it means there are more particles knocking about in the same volume. Similarly when the pressure of a gas is increased it means that the same number of particles occupies a smaller space. This makes collisions between the reactant particles more frequent.
Why does increasing surface area increase the rate?
If one of the reactants is a solid, then breaking it up into smaller pieces will increase its surface area to volume ratio. This means that for the same volume of the solid, the particles, around it will have more area to work on- so there will be collisions more frequently.
What is Le Chatelier’s Principle?
The idea that if you change the conditions of a reversible reaction at equilibrium and the system will try to counteract that change.
What are alkanes?
Alkanes have C-C single bonds, the general formula is Cn H2n+2. They are saturated compounds, each carbon atom forms 4 single covalent bonds.
What are the properties of hydrocarbons?
They get less viscous as they get shorter.
The shorter the carbon chain, the more volatile the hydrocarbon is (easier to turn into a gas) so the lower the boiling point.
The shorter the carbon chain, the more flammable the hydrocarbon is.
What’s the equation of complete combustion of hydrocarbon with oxygen?
hydrocarbon + oxygen → carbon dioxide + water (+energy)
What is crude oil?
A fossil fuel, it’s formed from the remains of plants and animals, mainly plankton. Over millions of years with high temperatures and pressure, the remains turn into crude oil which can be drilled up.
How is crude oil separated?
The oil is heated until most of it has turned into a gas, this then enters the fractionating column.
The column is hotter at the bottom and cooler at the top.
The long hydrocarbons have high boiling points, so they condense so much quicker at the bottom.
The crude oil is then separated into different fractions, where the different fractions have a similar amount of carbon bonds.
What are alkenes?
Have a C = C bond. The general formula is CnH2n. They burn with smoky flames, when they combust completely.
What is the incomplete combustion for alkenes?
alkene + oxygen → carbon + carbon monoxide + carbon dioxide + water
What do alkenes do to bromine water?
When orange bromine water is added to a saturated compound, like an alkane, no reaction will happen and it will stay bright orange.
If it is added to an alkene the bromine will add across the double bond, making a colourless dibromo-compound so the bromine water is decolourised.
What happens to alkenes when steam is reacted?
Alcohols are formed. E.g ethene + water → ethanol
What are polymers?
Polymers are long molecules formed when lots of small molecules called monomers join together. This reaction is called polymerisation.
