chemistry paper 2 mark scheme

chemistry paper 2 mark scheme crude oil is formed by the decomposition of... - correct answearsplankton describe how crude oil is formed - correct answearsplankton buried in mud over millions of years Describe how crude oil is separated into fractions by fractional distillation - correct answearscrude oil is heated hydrocarbons evaporate vapours / gases condense fractions have different boiling points describe the test for alkenes - correct answearstest : bromine water colour change : orange to colourless explain how a catalyst increases the rate of reaction - correct answearsprovides an alternative pathway which has a lower activation energy explain how a sample can be tested to show that carbon dioxide is not present in the mixture - correct answearsuse limewater should not turn milky / cloudy if carbon dioxide is not present explain how an equilibrium is reached - correct answearswhen the apparatus prevents the escape of reactants and products and the forward and reverse reactions occur at the same rate explain how distillation is used to obtain potable water from salty water - correct answearsheat salty water so water evaporates as water vapour cool the water vapour which condenses to form potable water explain how increasing the temperature affects the rate of reaction. - correct answearsrate increases becauses particles have more energy so there are more frequent collision