Unit 1(a) - Rates of Reaction Flashcards
(43 cards)
How can you speed up a reaction?
- Decreasing particle size of solid reactant - increased surface area
- Increasing concentration of reactant in solution - more particles
- Increasing temperature of reaction - higher kinetic energy
- Addition of a catalyst
How can you follow the rate of a reaction?
Measuring changes in conc, mass, and vol of reactants and products
What happens to the quantity of reactants/products during a reaction?
The quantity/concentration of reactants decreases and the quantity/concentration of products increases
What is the formula for average rate of reaction?
Av. rate = change in quantity/change in time
What is the formula for relative rate of reaction?
Rel. rate = 1/t
What kind of reaction can be used to investigate changing concentration and reaction rate?
Iodine ‘clock’ reaction
A time lapse occurs before a sudden end point is reached
Why are starch and sodium thiosulphate added to the mixture of an iodine clock reaction?
- iodine turns black in presence of starch, so marks an end point of reaction.
- Thiosulphate changes iodine molecules back into ions, using iodine up before colour forms. Once thiosulphate is all used up, the starch turns blue/black
What is the equation for the iodine clock reaction?
Hydrogen peroxide + hydrogen ions + iodide ions -> water + iodine molecules
What is the relationship between concentration and reaction rate?
As the concentration increases, the rate of reaction increases. The concentration is directly proportional to reaction rate
What reaction can be used to investigate changing temperature and reaction rate?
Oxalic acid and acidified potassium permanganate
What is the equation for the reaction between oxalic acid and potassium permanganate?
Oxalic acid + hydrogen ions + permanganate ions -> magnesium ions + carbon dioxide + water
What is the relationship between temperature and rate of reaction?
As the temperature increases, reaction rate increases. Rate of reaction is not directly proportional to temperature
According to collision theory, substances can only react if:
- Their particles collide with each other in the correct orientation
- Collision have enough energy to allow them to collide with enough force to break existing bonds
Why is it important that not all collisions result in a successful reaction?
All reactions would be instantaneous. Gentle collisions result in reactant particles bouncing apart unchanged
What experiment can be used to investigate collision theory with respect to concentration, particle size and temperature?
Marble (Calcium carbonate) + Hydrochloric acid
Marble and hydrochloric acid experiment: vary concentration of HCl
The surface of the marble will be hit more often by acid ions (more collisions per second) leading to a faster reaction.
The higher the concentration, the faster the reaction.
Marble and hydrochloric acid experiment: vary particle size of marble
Breaking up the solid increases surface area exposed to other reactant. Collisions can only take place on the surface of a reactant.
The smaller the particles, the greater the surface area so the faster the reaction.
Marble and hydrochloric acid experiment: vary temperature
Temperature is a measure of the average kinetic energy of particles. Increasing temperature causes reactant particles to move faster, so they collide more often and with greater Ek
The higher the temperature, the more frequent and energetic the collisions, so the faster the reaction
What is an exothermic reaction?
A chemical change which gives out heat energy to the surroundings
Give 3 examples of exothermic reactions
- Combustion of elements/carbon compounds/fuels
- Displacement of less reactive metals
- Neutralisation of acids by alkalis and reactive metals
In an exothermic reaction, how does the energy of the products compare with the energy of the reactants?
The products have less energy than the reactants
What is an endothermic reaction?
A chemical change which takes in heat energy from the surroundings
Give 3 examples of endothermic reactions
- Reaction of steam with hot coke to make water gas
- Neutralising ethanol acid with ammonium carbonate or sodium hydrogen carbonate
- Dissolving certain salts in water (ammonium nitrate, potassium nitrate)
In an endothermic reaction, how does the energy of the products compare with the energy of the reactants?
The products have more energy than the reactants
