Flashcards
Rates and Equilibrium, AQA Chapter 8
Cards in this deck (27)
- 1What is meant by the rate of a chemical reactionThe rate of a chemical reaction tells you how fast reactants turn into products
- 2Why the reaction rate is very important in the chemical industryAny industry process has to make money by producing useful products. This means the right amount of product needed must be made as cheaply as possible. Uf it takes too long to produce, it will be hard to make a profit when it is sold. The rate of the reaction must be fast enough to make it quickly but safely
- 3How to collect data on the rate of a chemical reaction•You can find out the rate of a chemical reaction by monitoring the amount of reactants used up over time
•Alternatively, you can find out the rate of reaction by measuring the amount of products made over time - 4How to calculate the mean rate of a reactionMean rate of reaction =
quantity of reactant used / time
or
quantity of product formed / time - 5How to calculate the rate of reaction at a specific timeTo calculate the rate of reaction at a specific time, draw the tangent to the curve, then calculate its gradient
- 6The factors that can affect the rate of a chemical reactionThere are four main factors which can affect the rate of chemical reactions:
temperature, surface area of solids, concentration of solutions or pressure of gases, and the pressure of a catalyst - 7Collision theoryParticles must collide, with a certain minimum amount of energy, before they can react
- 8Activation energy of a reactionThe minimum amount of energy that particles must have in order to react is called the activation energy
- 9How to use collision theory to explain the effect of surface area on reaction rateThe rate of a chemical reaction increases if the surface area to volume ratio of any solid reactants is increased. This increases the frequency of collisions between reacting particles
- 10How increasing the temperature affect the rate of reactionReactions happen more quickly as the temperature increases
- 11How to use the collision theory to explain why increasing the temperature affects the rate of reactionIncreasing the temperature increases the rate of reaction because particles collide more frequently and more energetically. More of the collisions occurring in a given time results in a reaction, because a higher proportion of particles have energy greater than the activation energy
- 12How, and why, increasing the concentration of reactants in solutions affects the rate of reactionIncreasing the concentration of reactants in a solution increases the rate of reaction because there are more particles of the reactants moving around in the same volume of solution. The more 'crowded together' the reactants particles are, the more likely it is that they will collide. SO the increased frequency of collisions results in a faster reaction
- 13How, and why, increasing the pressure of reacting gases affects the rate of reactionIncreasing the pressure of reacting gases has the same effect as increasing the concentration. Increasing the pressure squashes the gas particles more closely together. There are more particles of gas in a given space. This increases the chance that they will collide and react. So increasing the pressure produces more frequent collisions, which will increase the rate of the reaction
- 14What a catalyst isA catalyst is a substance that changes the rate of a reaction. However not changed chemically itself at the end of the reaction. A catalyst is not used up in the reaction, so it can be used over and over again. Different catalysts are needed for different reactions
- 15How catalysts workCatalysts increase rates of reaction by providing an alternative reaction pathway to the products, with a lower activation energy than the reaction without the catalyst present. So with a catalyst, a higher proportion of the reactant particles have sufficient energy to react. This means that the frequency of effective collisions increases and the rate of reaction speeds up
- 16Advantages of catalysts in industry•They help save money
Catalysts are often very expensive precious metals. It is usually cheaper to use a catalyst than pay for extra energy needed without one
•Help save the environment
Using high temperatures and pressures often involves burning fossil fuels. So operating at lower temperatures and pressures conserves these non-renewable resources - 17Disadvantages of catalystsCatalysts used in chemical plants eventually become 'poisoned', so that they do not work anymore. This happens because impurities in the reaction mixture combine with the catalyst and stop it working properly
- 18What a reversible reaction isIn a reversible reaction, the products of the reaction can react to make the original reactants
- 19How you can represent reversible reactionsYou can show a reversible reaction using the ⇌ sign
- 20What happens in the energy transfers in reversible reactionsIn reversible reactions, one reaction is exothermic and the other is endothermic. In any reversible reaction, the amount of energy transferred to the surroundings when the reaction goes in one direction is exactly equal to the energy transferred back when the reaction goes in the opposite direction
- 21How a reversible reaction in a closed system can be 'at equilibrium'In a closed system, the rate of the forward and reverse reactions is equal at equilibrium
- 22How the composition of an equilibrium mixture can be altered by changing conditions, such as contraceptionChanging the reaction conditions can change the amounts of products and reactants in a reaction mixture at equilibrium
- 23How changing the pressure affects reversible reactions involving gasesPressure can affect reversible reactions involving gases at equilibrium. Increasing the pressure favours the reaction that forms fewer molecules of gas. Decreasing the pressure favours the reaction that forms the greater number of molecules of gas
- 24How changing the temperature affects reversible reactionsYou can change the relative amount of products formed at equilibrium, by changing the temperature at which you carry out a reversible reaction. Increasing the temperature favours the endothermic reaction. Decreasing the temperature favours the exothermic reaction
- 25Affecting the composition of a equilibrium mixtureOne example of a reversible reaction is the reaction between iodine monochloride, ICl, and chlorine gas. Iodine monochloride is a brown liquid, while chlorine is a yellowish green gas. These substances can be reacted together to make yellow chystals of iodine trichloride, ICl3
- 26Le Châteiler's PrincipleYou can change the relative amounts of the reactants and products in a reacting mixture at equilibrium by changing the conditions. This is an application of Le Châtelier's Principle. Henry Louis Le Châteilier was a French chemist who observed equilibrium mixtures. He noticed that whenever a change in conditions is introduced to a system at equilibrium, the position of equilibrium shifts so as to cancel out the change. The change in conditions can be changes in concentration, pressure or temperature
- 27Why La Châteilier's principle is importantThe principle is very important in the chemical industry. In a process with a reversible reaction, industrial chemists need to find the conditions that give as much product as possible, in as short a time as possible
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- Year 9 Chemistry Flashcards on Rates and Equilibrium, AQA Chapter 8, created by Miles McIntosh on 14/01/2018.
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- Miles McIntosh
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