Rates of Reaction Flashcards
What is rate of reaction?
How fast the reactants are changed into products
Examples of slow reactions
Rusting
Chemical Weathering
Examples of moderate speed reactions
Magnesium reacting with an acid to produce a gentle stream of bubbles
Examples of fast reactions
Burning
Explosions
Graphs for Rate of reaction
The steeper the line on the graph the faster the rate of reaction
The quickest reactions have the steepest lines and become flat in the lest time
Collision Theory
The rate of chemical reactions depends on the collision frequency of reacting particles (the more collisions the faster) and energy transferred during a collision (the more energy the more chance it will be a successful collision)
Factors affecting Rate of Reaction
Temperature
Concentration of a solution or the pressure of gas
Surface area
Presence of a catalyst
Equation for Rate of Reaction
Amount of reactant used or amount of product former/time
Precipitation and Colour Change
Record the visual change in a reaction (e.g. colourless to opaque)
Observe a mark through the solution and measure how long it takes to disappear (e.g. the faster the mark disappears, the quicker the reaction)
How long it takes fro a solution to lose/gain its colour
Results can be subjective
Change in Mass
As the gas is released the disappearing mass (conservation of mass) can be measured on the balance. The faster the mass disappears the faster the reaction.
Measure the volume of gas given off
Use a gas syringe to measure the volume off gas given off.
The more gas given off the faster the rate of reaction.
Practical about concentration effecting rate of reaction (1)
-Add a fixed volume of hydrochloric acid to a conical flask and add it to the conical flask to e measured on a weighing scale
-Add magnesium ribbon to the acid and plug the top with cotton wool
-Use a stopwatch and record the mass on the balance at regular intervals.
-Repeat and calculate mean
-Use a different concentration of hydrochloric acid.
-Plot graph
Practical about concentration effecting rate of reaction (2)
-Add a set concentration of sodium thiosulfate to a conical flask
-Put the flask on a piece of paper with a black cross on it
-Add hydrochloric acid to the flask and start the stopwatch
-Time how long it takes for the black cross to disappear through the cloudy sulfur
-Repeat with different concentration
Equalibrium in a reaction
Negative feedback loops
Position of equalibrium depends on temperature, pressure and concentration
What is La Chatelier’s Principle?
The idea that is you change the conditions of a reversible reactions at equalibrium they system will counter the change (negative feedback)
La Chatelier’s Principle- Temperature
Decreasing the temperature will favour the exothermic reaction and more exothermic products
La Chatelier’s Principle- Pressure
Only changed the equalibrium involving gases
Increasing the pressure favours the reaction with the fewest molecules
La Chatelier’s Principle- Concentration
If you change the concentration of either the products or reactants the equation is no longer equalibrium.
If you increase the concentration of the reactants the system will make more products
