C8 Flashcards
Activation energy
The minimum energy needed for a reaction to take place
Anhydrous
Describes a substance that does not contain water
Atmosphere
The relatively thin layer of gases that surround planet Earth
Catalyst
A substance that speeds up a chemical reaction by providing a different pathway for the reaction that has a lower activation energy
than the reaction without the catalyst present. With a catalyst, a higher proportion of the reactant particles have sufficient energy to react, meaning the frequency of effective collisions(collisions resulting in a reaction) and the rate of reaction speeds up.
Climate change
The change in global weather patterns that could be caused by excess levels of greenhouse gases in the atmosphere
Closed system
A system in which no matter enters/leaves
Equilibrium
The point in a reversible reaction in which the forward and backward rates of reaction are the same, so the amount of substances in the remaining mixture remain constant
Hydrated
Describes a substance that contains water in its crystals
Le Châtelier’s Principle
When a change in conditions is introduced to a reversible reaction at equilibrium, the position of equilibrium shifts(between left and right) to counteract the change
A reversible reaction
A reaction in which the products can re-form the reactants
Precision
A precise measurement where there’s very little spread about the mean value
Examples of slow chemical reactions
Rusting of iron
Chemical weathering
Examples of moderately quick chemical reactions
The metal magnesium reacting with an acid to produce a gentle stream of bubbles
Examples of fast chemical reactions
Burning
Combustion of chemicals inside a firework exploding
Graphs for the rate of reaction
Over time, the line becomes less steep as the reactants are used up.
If graphs meet(converge) at the same level, they all produce the same amount of product although they take different times to produce it.
Rate of a chemical reaction
How fast the reactants are turned into products
How the collision theory impacts the rate
of reaction
The more collisions there are the faster the reaction is. Particles have to collide with enough energy for the collision to be successful.
Collision frequency
How often reacting particles collide
with enough energy to cause a reaction to take place
Factors affecting rates of reaction
Temperature
Concentration of solution/pressure of as
Surface area of solids
Presence of a catalyst
These all increase the number of successful collisions between the reacting particles, which increases the rate of reaction.
How does temperature affect the rate of reaction?
When the temperature is increased, energy is transferred to particles, so particles move faster, so collide with more frequently and enough energy for the reaction to occur.
Here, an increased proportion of particles exceeding the activation energy will have a greater effect on rate than the increased frequency of collisions.
How does concentration/pressure affect the rate of reaction?
If a solution is made more concentrated, there are more particles knocking about in the same volume of water and when the gas pressure increases, the same number of particles occupy a smaller space and the reactant particles are more crowded together, making collisions more frequent and likely
How does surface area affect the rate of reaction?
If one of the reactants is a solid, breaking it into smaller pieces means the particles around it have more area to work one - so there will be more frequent collisions. The larger the surface area to volume ratio, the faster the reaction.
How does using a catalyst affect the rate of reaction?
Catalysts decrease the activation energy needed for the reaction to occur by providing an alternative reaction pathway with a lower activation energy. Catalysts speed up the reaction and increase the rate of reaction
Rate of reaction=
Amount of reactant used/product formed divided by time
How to measure the rate of reaction using precipitation and colour change?
1)Can record visual change in reaction if the initial solution is transparent and the product is an opaque precipitate(clouding the solution).
2) Observe a mark through the solution and measure how long it takes for it to disappear - the faster the mark 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/gain its colour.
Disadvantages of measuring rate of reaction using precipitation and colour change?
Subjective results - people might not agree on point where mark disappears/solution changes colour
Can’t plot a rate of reaction graph from the results
How to use change of mass to measure the rate of reaction?
1) A mass balance is used to measure the speed of reaction producing a gas.
2) As a gas is released, the mass disappearing is measured on the balance.
3) The quicker the reading on the balance drops, the faster the reaction. This shows as the reaction takes place, the mass of the reaction mixture decreases. You can measure and record the mass at regular time intervals.
Safety: Wear eye protection
Equipment:
Cotton wool bung - putting cotton wool in the top of the flask lets the gas escape, but stops the acid spitting out
Marble chips and hydrochloric acid
Conical flask
Advantages of using changes in mass to measure the rates of reaction?
Most accurate of three methods due to mass balance.
If you take measurements at regular intervals, you can plot a rate of reaction graph
Disadvantages of using changes in mass to measure the rate of reaction?
Could release the gas straight into the room
How to use the volume of gas to measure the rate of reaction?
1) Can use 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