The Rate and Extent of Chemical Change Flashcards
What is Collision Theory?
Particles must collide with enough energy to react
Rate of Decay Factors
Temperature
Concentration of Solution / Pressure of Gas
Surface Area
Presence of a Catalyst
Rate of Reaction Equation
Rate of Reaction = Amount of reactant used or amount of product formed / Time
Measuring Rate of Reaction through Precipitation and Colour Change
1) You can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution
2) You can observe a mark through the solution and measure how long it takes for it to disappear - the faster it disappears, the quicker the reaction
3) If the reactants are coloured and the products are colourless, you can time how long it takes for the solution to lose its colour
4) The results are very subjective - different people might not agree over the exact point when the mark ‘disappears’ or the solution changes colour
Measuring Rate of Reaction through Change in Mass
1) Measuring the speed of a reaction that produces a gas can be carried out using a mass balance
2) As the gas is released, the mass disappearing is measured on the balance
3) The quicker the reading on the balance drops, the faster the reaction
4) If you take measurements at regular intervals, you can plot a rate of reaction graph and find the rate quite easily
5) This is the most accurate of the three methods because the mass balance is very accurate
Measuring Rate of Reaction through Volume of Gas Given off
1) This involves the use of a gas syringe to measure the volume of gas given off
2) The more gas given off during a given time interval, the faster the reaction
3) Gas syringes usually give volumes accurate to the nearest cm³, so they’re quite accurate. You can take measurements at regular intervals and plot a rate of reaction graph using this method too. You have to be quite careful though - if the reaction is too vigorous, you can easily blow the plunger out at the end of the syringe
Magnesium and HCl Rate of Reaction Required Practical
1) Start by adding a set volume of dilute hydrochloric acid to a conical flask
2) Now add some magnesium ribbon to the acid and quickly attach an empty gas syringe to the flask
3) Start the stopwatch. Take readings of the volume of gas in the gas syringe at regular intervals, recording your results in a table
4) Plot a graph with time on the x-axis and volume of gas produced on the y-axis
5) Repeat with more concentrated acid solutions. Variables such as the amount of magnesium ribbon and volume of acid used should be kept the same each time - only change the acid’s concentration . This is to make your experiment a fair test
6) The three graphs show that a higher concentration of acid gives a faster rate of reaction
Sodium Thiosulfate and HCl Rate of Reaction Required Practical
1) These two solutions are both clear solutions. They react together to form a yellow precipitate of sulfur
2) Start by adding a set volume of dilute sodium thiosulfate to a conical flask
3) Place the flask on a piece of paper with a black cross drawn on it. Add some dilute HCl to the flask and start the stopwatch
4) Now watch the black cross disappear through the cloudy sulfur and time how long it takes to go
5) The reaction can be repeated with solutions of either reactant at different concentrations. The depth of the liquid must be kept the same each time
6) These results show the effect of increasing the concentration of HCl on the rate of reaction, when added to an excess of sodium thiosulfate
7) The higher the concentration, the quicker the reaction and therefore the less time it takes for the mark to disappear
What is a Reversible Reaction?
Reactants ⇌ Products
Reactants can become Products
Products can become Reactants
What does an equilibrium position to the left mean?
Concentration of Products is greater than Reactants
What does an equilibrium position to the right mean?
Concentration of Reactants is greater than Products
