The rate and extent of chemical change

• How can the rate of reaction be found? [3] - Measuring the amount of reactants used - Measuring the amount of products formed - Measuring the time it takes for a reaction mixture to become opaque or change colour
• How do you measure the amounts of reactants used? - If one of the producs are a gas, measure the mass in grams of the reactant before and after the reaction takes place and the time it takes for the reaction to happen.
• What happens to the mass mixture when measuring the amount of reactants used? Mass of mixture will decrease
• What are the units for the rate of reaction given by? g/s
• How else can the amount of a reactant be measured by? Moles - As the reaction takes place the reactant is used up, so the amount of reactant remaining decreases
• How can the concentration of the reactant be calculated as? [2] The amount (mol) divided by the volume of the reaction mixture (dm3). It is measured in units of mol/dm3
• How do you measure the amount of products formed? - If one of the product is a gas, measure the total volume of gas produced in cubic cm (cm3) with a gas syringe and the time it takes for the reaction to happen.
• What will the units for measuring the amount of products formed by given as? - Given as cm3/s
• What do you do to measure the time it takes for a reaction mixture to become opaque or change colour? Time how long it takes for the mixture to change colour
• How do chemical reactions occur? When reacting particles colide with each other with sufficient energy
• What is activation energy? The minimum amount of energy required to cause a reaction
• What are four important factors that affect the rate of reaction? [4] - Temperature - Concentration - Surface Area - Catalysts
• What does a hot reaction mixture do to the rate of reaction? In a hot reaction mixture the particles move more quickly
• What does a high concentration of the reactant do to the rate of reaction? At higher concentrations, the particles are crowded closer together
• What happens if you increase the pressure of the reacting gases? The frequency of the collisions increases
• What do small pieces of a solid reactant have? Small pieces of a solid reactant have a large surface area in relation to their volume
• What are plotted graphs used for? Show the progress of a chemical reaction
• What 3 key things are there to remember about plotting graphs? [3] - Steeper the line = faster the reaction - When one reactant is used up, the reaction stops (the line becomes horizontal) - THe same amount of product is formed from the same amount of reactants, regardless of rates
• What is a catalyst? A substance that increases the rate of a chemical reaction without being used up
• Do catalysts shift the equilibrium? No
• What does a catalyst do? [4] - Reduce the amount of energy needed for a successful collision - Makes more collisions successful - Speeds up the reaction - Provides a surface for the molecules to attach to (increases their chance of bumping into each other)
• What do enzymes act as? As catalysts in a biological system
• Why is increasing the rate of chemical reactions important in the industry? Because it helps reduce costs
• What are reversible reactions? In a reversible reaction, the products can react to form the original reactants
• How can the direction of a reversible reaction be changed? By changing the conditions
• What happens to the reactants and products in a closed system? [2] - No reactants removed - No products added
• What happens when a reversible reaction occurs in a closed system? A equilibrium is achieved when the rate of the forward reaction is equal to the rate of the backward reaction in a closed system
• What do the relative amounts of all the reacting substances at equilibrium depend on? Depend on the conditions of the reaction
• What does Le Chatelier's Principle state? If a system in a equilibrium is subjected to a change in conditions, then the system shifts to resist the change
• What happens to the yield, if the temperature is raised in an exothermic reaction? The yield decreases
• What happens if the temperature is lowered in a exothermic reaction? The yield increases
• What happens if the temperature is raised in an endothermic reaction? The yield increases
• What happens if the temperature is lowered in an endothermic reaction? The yield decreases
• What happens in reactions involving gases? [2] - An increase in pressure favours the reaction that produces the least number of gas molecules - A decrease in pressure favours the reaction that produces the greater number of gas molecules
• What happens if the concentration of one of the reactants or products is changed? [2] - System no longer in equilibrium - System adjusts until it can reach equilibrium once more
• What happens to the position of the equilibrium if the concentration of one of the reactants is increased? It shifts so that more products are formed until equilibrium is reached again
• What happens to the position of the equilibrium if the concentration of one of the reactants is decreased? It shifts so that more reactants are formed until equilibrium is reached again
• In a hot reaction mixture, the particles move quickly. What does this mean for when they collide? [3] - Collide more often and with greater energy - So more collisions are successful
• If the the concentration is high, then the particles are crowded closer together. What does this do to the collision rate? They collide more often, so there are more successful collisions
• What does a large surface area mean for the reacting particle? [2] - More particles are exposed and available for collisions - More collisions and faster reaction