The rate and extent of chemical change Flashcards
What is collision theory?
The rate of a chemical reaction depends on the collision frequency of the particles and the energy transferred during a collision (enough energy needs to be transferred for success).
What is the rate of reaction?
How fast it takes for the reactants to change into products.
What factors affect the rate of reaction?
Surface area, pressure/concentration, temperature and use of a catalyst.
What is the equation to find the rate of reaction?
Rate of reaction = amount of react used or amount of product formed/ time
What measurements do you use?
Solids you use grams (g) and liquids you use cm^3 and time is measured in seconds.
What are three ways to measure the rate of reaction?
Change in mass, precipitation and colour change, volume of gas given off.
What are some limitations when using precipitation and colour change?
As you are simply observing something turning from one colour to another or something disappearing or appearing it can be very subjective. It is also impossible to plot a reaction graph.
What are two investigations which look into the effect of concentration on the rate of the reaction?
Reacting magnesium and hydrochloric acid to produce hydrogen and reacting sodium thiosulfate and hydrochloric acid to produce a cloudy precipitate.
What is the method for reacting magnesium and HCl to produce hydrogen?
Add a fixed volume of dilute HCl to a conical flask and place on a mass balance. Add magnesium ribbon and plug the flask with cotton wool. Start the stopwatch to record the mass on the balance and record at regular intervals. Repeat with a more concentrated solution. But do not change anything else.
What is the outcome of the HCl and magnesium experiment.
The higher the concentration the faster the reaction.
What is the method for sodium thiosulfate and HCl?
Both chemicals are clear and they react to form a yellow precipitate and sulfur. First add dilute sodium thiosulfate to a flask. Place the flask on paper with a cross on it. Add dilute HCl and start the timer. Now watch how the black cross underneath the flask disappear through the cloudy sulfur. You can change the concentration of the reactants now whilst keeping one the same and the depth of the water the same.
How do you calculate a mean reaction rate from a graph?
Work out the overall change in the y-value and divide it by the whole time take,
How do you calculate the reacction rate at a particular point?
Draw a tangent at the point and find the gradient at this point.
What is a reversible reaction?
Where the products can react to form the reactants.
What is equilibrium?
When a system has the reactants going at the same rate as the backward reaction. At equilibrium both reactions are still happening but there is no overall effect and the concentrations are the same.
Where can equilibrium only take place?
Only in a closed system where no reactants or products can escape.
Are the products and reactants amounts equal at equilibrium.
No.
What happens if equilibrium lies to the right?
The concentration of products is greater than that if the reactants.
What happens if eqilbirum lies to the left?
The concentration of the reactants is greater than that of the products.
What does the position equilbrium depend on?
Temperature, pressure(only in gases) and concentration.
In reversible reactions are there exothermic reactions?
In one direction there will be an exothermic reaction and an endothermic one in the other.
What will reversible reactions do if there is a change in the conditions?
They will try to counteract it.
What will happen if you decrease the temperature?
The equilibrium will move in the exothermic direction to produce more heat.
What will happen if you increase the temperature?
The equilibrium will move in the endothermic direction to decrease it.
