chemistry paper 2

• What are hydrocarbons? Hydrocarbons are moleucules made up only of hydrogen and carbon atoms.
• What is the formula of alkanes?
• Structures of methane, ethane, propane and butane
• What is crude oil? Crude oil is a finite resource that is found in the Earth's crust. It is the remains of organisms that lived and died millions of years ago - mainly plankton which was buried in mud. Crude oil is a complex mixture of hydrocarbons. The carbon atoms in these molecules are joined together in chains and rings.
• Formula for the combustion of hydrocarbons
• What are alkanes? Alkanes are a family of hydrocarbons that are described as saturated hydrocarbons. This means that their carbon atoms are joined to each other by single bonds. This makes them relatively unreactive, apart from their reaction with oxygen in the air - which we call burning or combustion.
• What is viscosity? Viscosity tells us the thickness of a fluid
• Formula for alkenes
• What is cracking? Cracking is a reaction in which larger saturated hydrocarbon molecules are broken down into smaller, more useful hydrocarbon molecules, some of which are unsaturated.
• What are alkenes? Alkenes are a homologous series of hydrocarbons that contain a carbon-carbon double bond. This means that they are unsaturated.
• Trends in the long-chain/small-chain of hydrocarbons
• What is a functional group? Functional group is a group of atoms that determine the chemical properties of a compound
• What is fractional distillation? Fractional distillation is the process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms. We call these groups of hydrocarbons “fractions”.
• Why do longer chain hydrocarbons have a higher boiling point? Because they have greater intermolecular forces
• Thermal/Steam cracking vs Catalytic cracking - Thermal cracking uses a high temperature of over 800°C and no catalyst - Catalytic cracking uses a temperature of 550°C and a catalyst
• Fractional distialltion process (6 marks) 1) Crude oil is heated and fed into the bottom of a tail fractioning column as hot vapor 2) Hydrocarbon gases rise up the column 3) Gases condense when they reach their certain temperature of their boiling points 4) Different fractions are collected as liquids at certain levels 5) Small chain hydrocarbons are removed at the top of the fractioning column where it is cooler 6) Long chain hydrocarbons are removed at the top of the fractioning column where it is hotter
• What does incomplete combustion produce? Incomplete combustion is when there is a lack of oxygen ; this causes a toxic gas called carbon monoxide to be produced
• Describe a positive test for each of the products of complete combustion
• What physical property allows distillation to seperate different molecules? Boiling point
• What is the rate of reaction? How fast reactants turn into products
• What is reaction rate important in? The chemical industry and your body
• Why is reaction rate important in the chemical industry? To make sure products are made quickly and cheaply
• What are the two ways you can work out the rate of a chemical reaction? How quickly the reactants are used up and how quickly the products are made
• What are the three techniques you can use to get the rate of a reaction? - Change in mass - Change in color - Increase/decrease in volume
• How can you calculate the rate of a reaction at a given time? Drawing a tangent to the curve at that point, constructing a right angled triangle and calculating the gradient
• How can you calculate the mean rate of reaction after a given time?
• What are the four main factors which affect the rate of chemical reactions? - Temperature - Surface area - Concentration - Pressure
• What is collision theory? The reacting particles do not only have to bump into each other but also need to colldie with enough energy to cause a reaction to take place
• What are the two ways reactions are more likely to happen between reactant particles? By increasing the frequency of reacting particles colliding with each other and increasing the energy you have when they collide
• You can compare solids wth different surface areas quantitatively by looking at their _____ surface area to volume ratio
• Why is food cooled? To slow unwanted chemical reactions
• What are the two reasons why raising temperature increases the rate of reaction? Particles collide more often and particles collide with more energy
• What happens when particles collide more frequently? There are more chances for them to react, increasing the rate of reaction
• Particles that are moving around more quickly have more ___ energy
• What has a greater effect on the rate of reaction than the increased frequency of collisions? An increased proportion of particles exceeding the activation energy
• Why does increasing the concentration of reactants in a solution increase the rate of reaction? Because there are more particles of the reactants moving around in the same volume of solution.
• What does increased pressure do to the rate of reaction? It squashes gas particles more closely together, increasing the chance they will collide and react
• How can you investigate the effect of changing concentration? By reacting marble chips with different concentrations of hydrochloric acid
• How would you find the rate of reaction when reacting marble chips with hydrochloric acid? By plotting the volume of carbon dioxide gas given off as the reaction progresses over time
• What is a catalyst? A substance that changes the rate of a reaction without being changed chemically itself