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CC15,16,17Foundation
GCSE Combined Science Chemistry
| Question | Answer |
|---|---|
| State what is meant by an exothermic reaction. | A reaction that transfers energy to the surroundings. |
| What happens to the temperature of the surroundings during an exothermic reaction? | It increases |
| Give three examples of exothermic reactions | Neutralisation, Displacement, Combustion. |
| State what is meant by an endothermic reaction | A reaction that absorbs energy from the surroundings |
| What happens to the temperature of the surroundings during an exothermic reaction? | It decreases |
| Describe the reaction profile of an exothermic reaction. | The reactants have more energy than the products, so the reactant line on the graph is higher than the product line. |
| Describe the reaction profile of an endothermic reaction. | The reactants have less energy than the products, so the reactant line on the graph is lower than the product line. |
| Describe the five steps of a practical to measure the energy change | "1. Sit a polystyrene beaker inside a glass beaker (insulation) 2. Measure the starting temperature of the reactants. 3. Mix the reactants in the polystyrene beaker 4. Cover with lid fitted with a thermometer 5. Monitor and record the highest or lowe |
| " Explain what happens to the bonds in a chemical reaction. | During chemical reactions, chemical bonds in the reactants are broken and bonds in the products are formed |
| State which of bond breaking and bond forming gives out energy (exothermic) and which takes in energy (endothermic) | "Bond breaking is Endothermic Bond forming is Exothermic. |
| " Describe how the energy change in a reaction is linked to bond breaking and bond forming. | The energy change in a reaction is the difference between the energy required to break the bonds in the reactants and the energy released by making bonds in the products |
| How do catalysts speed up reactions? | They provide another route for the reaction to take place which has a lower activation energy. |
| How does the law of conservation of energy apply to chemistry? | In all chemical reactions, energy is either transferred to the surroundings or from the surroundings. |
| What is an exothermic reaction? | A reaction where energy is transferred to the surroundings. |
| Give two examples of exothermic reactions. | Combustion, respiration |
| What happens to the temperature of the surroundings during an exothermic reaction? | They increase. The thermometer is included in "the surroundings" so shows the temperature increasing. |
| What is an endothermic reaction? | A reaction where energy is transferred from the surroundings. |
| Give two examples of endothermic reactions. | Thermal decomposition reactions, citric acid and sodium hydrogencarbonate. |
| What happens to the temperature of the surroundings during an endothermic reaction? | They decrease. The thermometer is included in "the surroundings" so shows the temperature decreasing. |
| State two uses of exothermic reactions | Self-heating cans, hand warmers |
| State two uses of endothermic reactions | Some cooling sports injury packs |
| What are reactants? | The substances involved in a chemical reaction |
| What are products? | The substances formed when reactants have a chemical reaction |
| What is a reaction profile? | A diagram which shows whether the reactants have more or less energy than the products. |
| If the reactants have more energy than the products, what kind of a reaction must have taken place? | An exothermic one. The missing energy has been transferred to the surroundings. |
| If the reactants have less energy than the products, what kind of a reaction must have taken place? | An endothermic one. The extra energy has been taken in by the surroundings. |
| Is breaking bonds endothermic or exothermic? | Endothermic. Chemical bonds are strong so require energy to break (like when you have to put energy in to separate magnets from each other) |
| Define the activation energy of a chemical reaction. | The minimum amount of energy that must be provided to compounds to result in a chemical reaction. |
| Is making bonds endothermic or exothermic? | Exothermic. Energy is released when chemical bonds are formed (like how two magnets move together when close and generate kinetic energy) |
| How do we work out the overall energy change of a reaction? | Work out the difference between the energy needed to break all the bonds in the reactants and the energy released to form all the bonds in the products. |
| If more heat energy is released forming bonds than is required for breaking bonds in a reaction what kind of reaction is it? | exothermic |
| If less heat energy is released forming bonds than is required for breaking bonds in a reaction what kind of reaction is it? | endothermic |
| What is a hydrocarbon? | A compound containing only hydrogen and carbon. |
| Describe the nature of crude oil. | A thick brown liquid made of a mixture of many different hydrocarbons found in deposits underground. |
| Describe the properties of the substances in crude oil. | Most of the hydrocarbons in crude oil are liquids, but each of them has a different boiling point. |
| State the two most important uses of crude oil. | Fuel, feedstock (supply of basic chemicals) for the chemical industry. |
| Crude oil is a finite resource. What does that mean? | There is a limited amount: at some point it will run out. |
| What is fractional distillation? | A type of distillation used to separate mixtures of two or more liquids. It separates compounds according to their boiling point. |
| Describe the 3 steps of fractional distillation. | "• Crude oil is passed through a heater to heat it to about 400OC so that nearly everything is a gas. • The hot gases rise up the fractionating column until cool enough to condense. • The separated liquids and gases collected at different temperatures. |
| " List the main fractions in order from those made up of the smallest molecules to the largest molecules. | Gases, petrol, kerosene, diesel oil, fuel oil, and bitumen. |
| What is the viscosity of a liquid? | How easily a fluid flows –lower viscosity = runnier. |
| How do the boiling point, viscosity and ease of ignition of the fractions of crude oil change as the molecules get larger? | "Lowest to highest boiling point Lowest to highest viscosity Easiest to hardest ignition |
| " What are the uses of Fuel Gases, Petrol, and Kerosene | " • Used for heating and cooking. • Used as a fuel for cars. • Fuel for aircraft |
| " What are the uses of Diesel oil Fuel Oil Bitumen | " • Fuel for lorries and trains • Fuel for ships and power stations • Surfacing roads and roofs |
| " What is a homologous series? | A group of closely related compounds with molecular formulae that differ only in the number of ‘CH2’s. |
| What is an alkane? | A hydrocarbon with only single bonds |
| Name the first four alkanes and write their formula | "Methane – CH4 Ethane – C2H6 Propane – C3H8 Butane – C4H10 |
| " How do boiling point, viscosity and flammability of alkanes change as their molecules get longer? | "• The longer the alkane the higher the boiling point • The longer the alkane the more viscous it is. The longer the alkane the less flammable it is. |
| " What is complete combustion? | • Combustion that produces only water and carbon dioxide |
| What is incomplete combustion? | Combustion that produces carbon monoxide or carbon as well as carbon dioxide and water. |
| Why does incomplete combustion occur? | When there is not enough oxygen for all of the reactants to be fully oxidised. |
| How does carbon monoxide kill? | It sticks to haemoglobin in the blood which prevents it from carrying oxygen. |
| What are the main problems caused by soot? | Causes lung problems when breathed in. Blackens and dirties buildings |
| What is acid rain? | Rain with a pH lower than 5.2 |
| Name three effects of acid rain. | "• Soil becomes too acidic for crops and plants to grow well • Acid in rivers and lakes prevents fish eggs from hatching and kills some insects. • Acid rain increases corrosion of limestone which damages buildings and statues |
| " What are the products of cracking? | • An alkane and a alkene |
| Why is cracking useful? | There is more demand for shorter hydrocarbons – such as petrol and gas – than longer ones such as bitumen. |
| What is an alkene? | A hydrocarbon containing a C=C double bond. |
| What is crude oil? | A mixture of hydrocarbons |
| What is a finite resource? Why is crude oil a finite resource? | One that will run out. Because it takes longer to form than the rate at which we are using it up |
| What is a hydrocarbon? | A compound made of atoms of carbon and hydrogen only |
| What is an alkane? | A hydrocarbon with only single bonds |
| Name the first four alkanes | Methane, ethane, propane, butane |
| What is the general formula for alkanes? | CnH2n+2 (the n and 2n are small) |
| How does boiling point change with the length of an alkane? | The longer the alkane, the higher its boiling point |
| How does viscosity change with the length of an alkane? | The longer the alkane, the more viscous (the thicker) it is |
| How does flammability change with the length of an alkane? | The longer the alkane, the less flammable it is |
| What is fractional distillation? | A process used to separate mixtures of substances with different boiling points |
| What are the steps involved in fractional distillation? | Crude oil is vaporised, different molecules rise up the fractionating column and cool down. Condense at different points on the column. |
| Why is fractional distillation important? | Because the different fractions have different uses |
| What is a fuel? | A substance which when reacted with oxygen releases energy |
| Name five fuels we obtain from crude oil | Petrol, diesel oil, kerosene, fuel oil and liquefied petroleum gases |
| What other uses are there for products of fractional distillation? | Solvents, lubricants, polymers and detergents |
| What is combustion? | The reaction of a fuel with oxygen |
| What are the products of complete combustion? | Carbon dioxide and water |
| When does incomplete combustion occur? | When there is not enough oxygen present |
| What is formed in incomplete combustion | Carbon monoxide |
| Why is carbon monoxide dangerous | It is toxic, taken up by red blood cells in preference to oxygen. |
| What is cracking? | The process of breaking down a long hydrocarbon into smaller hydrocarbons |
| What are the products of cracking? | Short alkanes and alkenes |
| Why is cracking important? | Because smaller hydrocarbons are more useful than longer ones |
| What are alkenes | A hydrocarbon with a double bond |
| What are alkenes used for? | As a starting material to make more useful chemicals |
| What is the general formula for alkenes? | CnH2n |
| What are the first four alkenes? | Ethene, propene, butene, pentene |
| What do members of a homologous series have in common? | Same general formula, differ by CH2 for neighbouring compounds in the series, boiling points increase with chain length, have similar chemical properties and reactions. |
| How is sulphur dioxide produced? | Sulphur impurities in fuels form it when the fuel is burnt |
| What happens when the sulphur dioxide dissolves in rain water? | Acid rain is formed |
| How are oxides of nitrogen formed? | When the nitrogen and oxygen in the air react together at the high temperatures created in combustion engines |
| State three advantages of hydrogen fuel cells over petrol | Do not need to be recharged, no pollutants are produced only H2O, water is a renewable resource |
| State three disadvantages of hydrogen fuel cells over petrol | Hydrogen is highly flammable, hydrogen is sometimes produced through non-renewable means, hydrogen is difficult to store and transport |
| How does ease of ignition change with the length of an alkane? | The longer the alkane, the harder it is to ignite. |
| How are members of a homologous series different from each other? | Their chain length differs by a number of CH2 |
| Where do petrol, kerosene and diesel oil come from? | They are obtained by fractional distillation of crude oil |
| Where does methane come from? | It is found in natural gas? |
| Are petrol, kerosene, diesel and methane renewable or non renewable? | non-renewable |
| What gases make up the earths early atmosphere? | mainly carbon dioxide and water vapour with little or no oxygen |
| What is responisble for earths early atmosphere? | Volcanoes |
| What happened to the water vapour in the earths atmosphere | The earth cooled down and the water vapour condensed to form liquid water, which formed the oceans |
| How did the levels of carbon dioxide in the early atmosphere start to deacrease | They dissolved into the newly formed oceans |
| What did sea creatures do with the dissolved carbon dioxide. What effect did this have on the atmosphere | Sea creatures used dissolved carbon dioxide to produce shells of calcium carbonate. This meant more carbon dioxide could be dissolved in the oceans from the atmosphere. |
| How else did some organism reduce the levels of carbon dioxide in the atmosphere? | They used it in photosynthesis which released oxygen into the atmosphere |
| What is the test for oxygen | take a glowing splint and place into oxygen it will relight |
| What is the greenhouse effect? | When gases in the atmopshere absorb infra-red energy from the earth which causes the atmosphere temperature to increase |
| What are the 3 most common greenhouse gases? | Carbon dioxide, Water and methane |
| What is global warming? | The increase in the earths average temperature likely to be caused by increase in carbon dioxide |
| What is climate change | Changes to the average weather conditions around the world |
| What evidence is there for global warming? | There is a close correlation between levels of carbon dioxide and average global temperature |
| What are some effects of climate change? | Melting of polar ice caps, changing of natural habitats and change of normal weather patterns |
| How can the effects of climate change be limited? | Use less fossil fuels by using renewable energy resources. Capture carbon dioxide from the atmosphere |
| How can oxygen be tested for? | Relights a glowing splint |
| What gases made up the Earths initial atmosphere | Large amount of carbon dioxide, water vapour, small amounts of other gases |
| What happened to the water vapour as the earth cooled? | Water vapour condensed forming oceans |
| What affect did the formation of the oceans have on the amount of carbon dioxide in the atmosphere? | Carbon dioxide dissolves in water so some dissolved and the amount in the atmosphere decreased |
| How did the growth of primitive plant affect the atmosphere? | They used carbon dioxide and released oxygen in photosynthesis |
| What is the composition of our atmosphere today? | Nitrogen about 78%, Oxygen 21%, 1% other gases |
| Name 3 greenhouse gases | Carbon dioxide, methane and water vapour |
| What is the greenhouse effect | Greenhouse gases absorb heat radiated from the earth and release it keeping the earth warm |
| Name 2 effects of global warming | Polar ice caps melting, sea levels rising |
| Where did the gases that fomed our early atmosphere come from? | They were produced by volcanic activity. |
| What gas, in today's atmosphere was missing from our early atmosphere? | oxygen |
| What does correlation mean? | There is a link between them. (eg. As one increases so does the other) |
| When did oxygen begin to be formed in our atmosphere? | When the first plants began photosynthesising |
| What do greenhouse gases do? | Trap heat in our atmosphere |
| Name one man made cause of the greenhouse effect | Deforestation |
| What has happened to the amount of carbon dioxide in our atmosphere in the last 200 years? | It has increased |
| What human activity might have increased the amount of carbon dioxide in our atmosphere? | Burning fossil fuels |
| What human activity, other than burning fossil fuels, might have increased the amount of carbon dioxide in our atmosphere? | Respiration (as population increases so does this) |
| If a sample of the atmosphere is reaccted with copper, what gas will react? | Oxygen |
| If all the oxygen is removed from a sample of the atmosphere how much is removed? | 0.21 |
Created by:
Davenant Foundation School