Rates And Extent Of Chemical Change Flashcards
Reactions
Reactions can go at all sorts of rates
The rate of chemical reaction depends on:
The collision frequency, the more collisions there are there faster the reaction
The energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful
Name the factors affecting rate of reactions
More collisions increase the rate of reaction
Increasing the temperature increase the rate
Increasing the surface area increase the rate
Using a catalyst increase the rate
Equation of rate of reaction
Rate of reaction = Amount of reactant used or amount of product formed / Time
There are three ways to measure the rate of reacriom
Precipitation and colour change
Change in mass
The volume of gas given off
Precipitation and colour change
You can record the visual change in a reaction if the initial solution is transparent and and the product is a precipitate which clouds the solution.
Change in mass (usually gas given off)
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 a balance.
3) the quicker the reading on the balance drops, the faster the reaction
The volume of gas given off
1) use a gas syringe to measure the volume of gas given iff
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 cm^3 , so they are quite accurate
What are the two rates experiment?
1) Magnesium and hydrochloric acid react to produce hydrogen gas
2) Sodium Thiosulfate and Hydrochloric acid produce a cloudy precipitate
Magnesium and HCl react to produce Hydrogen gas
1) start by adding a set volume of dilute hydrochloric acid to a conical flask and carefully place on a mass balance
2) now add some magnesium ribbon to the acid and quickly plug the flask with cotton wool
3) start the stopwatch and record the mass on the balance. Take readings of the mass at regular intervals
Sodium Thiosulfate and HCl produce a cloudy precipitate
These two chemical are both clear solutions. They react together to form a yellow precipitate of sulfur.
1) start by adding a set volume of dilute sodium thiosulfate to a conical flask
2) 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
3) now watch the black cross disappear through the cloudy sulfur and time how long it takes to go .
What is meant by if a system is at equilibrium?
When the forward and reverse reaction is happening at the same rate.
Reversible reactions will reach equilibrium
The forward reaction will slow down and the backward reaction will speed up. After a while the forward reaction will be going at exactly the same rate as the backward one - the system is at equilibrium.
Reversible reactions can be endothermic and exothermic
If the reaction is endothermic in one direction it will be exothermic in the other.
What is the idea of 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 that change.
