Paper 2 Model Answers

• distillation can be used to produce potable water from salty water
• a hydrocarbon is a molecule made up of carbon and hydrogen atoms only
• the amounts of nitrogen and oxygen in the earth's atmosphere increased; nitrogen increased due to emission from volcanoes and oxygen increased due to photosynthesis
• coal was formed from the CO2 present in the earth's early atmosphere because CO2 is used during photosynthesis in trees, which died and decompressed over millions of years
• during the combustion of 1kg of coal and 1kg of natural gas, coal produces more CO2 because coal has a higher proportion of carbon
• bioleaching uses bacteria to produce solutions containing copper compounds, then the copper is obtained by displacement or electrolysis
• in biological systems, a catalyst is an enzyme
• a catalyst increases the rate of reaction because it provides a different reaction pathway which has a lower activation energy
• using Le Chatelier's principle, scientists can predict the effects of changing conditions on the position of an equilibrium in a closed system
• a reversible chemical reaction can reach equilibrium when the forwards and reverse reactions have the same rate in apparatus, which prevents the escape of reactions and products
• N2 + 3H2 => 2NH3 : by increasing the pressure on the yield of ammonia, the yield increases because there are more moles of gas on the left hand side
• by increasing the temperature on the yield of ammonia, the yield decreases because the system shifts in the endothermic direction