C6

• The rate of a chemical reaction is how fast the reactants changed to products
• On a graph the steeper the line the faster rate of reaction
• Flat lines on a graph show the reaction is finished
• what are the factors affecting rate of reaction

  Temperature, concentration/pressure, surface area, catalyst
• Increasing the temp means particles move quicker and they're going to collide more frequently, the faster they move the more energy they have and so more of the collisions will have enough energy for a reaction to happen
• Increasing the concentration or pressure means the particles are closer together and have more frequent collisions
• Increasing the surface area is like increasing it's surface area:volume ratio, meaning same volume of solid has more area to work with, meaning more frequent collisions
• Using a catalyst lowers the activation energy needed for a reaction to occur by providing an alternative reaction pathway with lower activation energy
• The equation for rate of reaction = amount of reactant used / time
• Amount of reactant used and amount of product formed are equal
• Units for rate of reaction are in cm3/s or g/s
• When a product or reactant is a gas its measured in cm3
• When a product or reactant is a solid it's usually measured in grams
• Time is measured in seconds
• You an also measure amount of product or reactant in moles so unit could be mol/s
• There a 3 different ways of measuring rate of reaction
• Precipitation and colour change can be used to measure rate of reaction, by recording the visual change or observe a mark and measure how long it takes to disappear, but results are subjunctive
• subjunctive means different people might not agree on an exact point
• A change in mass can be used to measure rate of reaction that releases a gas, with a beaker on a mass balance and cotton wool in the neck.

  As gas is released mass disappearing is measured on the balance, quicker number drops=faster reaction

  Can be done at regular intervals to produce graph

  Most accurate method out of the 3, but releasing gas straight into the room is a disadvantage
• The volume of gas given off can also be used for measuring rate of reaction. Done using a gas syringe to measure volume given off, more gas given off during a time interval the faster the reaction.

  Can also plot graph by measuring at regular intervals.

  Must be careful that the reaction isn't too vigorous as can blow plunger out of syringe
• Practical-

  Magnesium and Hydrochloric Acid react to produce Hydrogen gas

  Add a set volume of dilute HCl to a conical flask, then magnesium ribbon to acid and then quickly attach an empty gas syringe to flask. Start stopwatch and take readings at regular intervals, plot results in table and graph
• Equilibrium is only reached if the reversible reaction takes place in a closed system meaning nothing can get in or out
• the position of equilibrium can be left or right shifted by changing the concentration of reactants or products, temperature or pressure
• when a reaction is at equilibrium it doesn't mean the amounts of reactants and products are equal
• If the equilibrium lies to the right, the concentration of products is greater than the concentration of reactants
• If the equilibrium lies to the left , the concentration of reactants is greater than the concentration of products
• Reversible reactions can be endothermic and exothermic
• Le Chatelier's principle is the idea that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract the change
• Le Chatelier's principle can be used to predict the effect of changing the conditions of a reaction
• Reversible reactions try to counteract changes like change of temperature
• Reversible reactions try to counteract changes of pressure
• Reversible reactions try to counteract changes of concentration
• All reactions are exothermic one direction and endothermic the other
• If you decrease the temp, equilibrium will move in the exothermic direction to produce more heat, meaning you'll get more products for exothermic reaction. If you raise temp, equilibrium will move in the endothermic direction to produce less heat, meaning you'll get less products for endothermic reaction.
• Increasing the pressure only effects equilibrium involving gas, by increasing the pressure the equilibrium tries to reduce it, moving in the direction where there are fewer molecules of gas
• Decreasing the pressure, the equilibrium tries to increase it and it moves in the direction where there are more molecules of gas
• You can use the balanced symbol equation to see which side has more molecules of gas
• By changing concentration of either reactants or products the system is no longer at equilibrium, so it responds to try bring it back to equilibrium . By increasing the concentration of reactants the system tries to decrease it by making more products. By decreasing concentration of products system tries to increase it again by reducing amount of reactants
• Haber process =N2 + 3H2 ---2NH3 ammonia example of reversible
• Increasing temp favours the endothermic reaction