Topic 6 - The Rate and Extent of Chemical Change (1)
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RATES OF REACTION: What is the rate of reaction?
how fast the reactants are changed into products
RATES OF REACTION: Give two examples of slow reactions?
• the rusting of iron • chemical weathering (like acid rain damage to limestone buildings)
RATES OF REACTION: Give an example of a moderate speed reaction?
metal magnesium reacting with an acid to produce a gentle stream of bubbles
RATES OF REACTION: Give 2 examples of fast reactions?
• burning • explosions (explosion are over in a fraction of a second)
RATES OF REACTION: What 2 things can you measure to calculate the rate of reaction?
• the amount of product formed • the amount of reactant used up
RATES OF REACTION: On a graph, what does a steep line show?
a fast rate of reaction
RATES OF REACTION: On a graph, what does the line becoming less steep show?
the reactants are being used up
RATES OF REACTION: How do graphs look for the quickest reactions?
• steepest lines • become flat in the least time
RATES OF REACTION: Explain how reaction rates are determined using collision frequency?
The rate of a chemical reaction depends on: 1) The collision frequency of reacting particles. The more collisions, the faster the reaction is. 2) The energy transferred during a collision. Particles have to collide with enough energy for the collision to be successful (a successful collision is one tht ends in the particles reacting to form products)
RATES OF REACTION: What is the activation energy?
the minimum amount of energy that particles need to react (particles need this much energy to break the bonds in the reactants to start the reaction)
RATES OF REACTION: What will factors that increase the number of collisions or energy the particles collide with do for the rate of reaction?
increase it
RATES OF REACTION: What are the 4 factors that affect rate of reaction?
• temperature • the concentration of a solution or the pressure of gas • surface area - changes depending on the size of the lumps of a solid • the presence of a catalyst
RATES OF REACTION: Why do certain factors increase the rate of reaction?
they increase the number of successful collisions between the reacting particles
RATES OF REACTION: Why does an increase in temperature increase the rate of reaction?
• particles move faster • so they collide more frequently • they also have more energy, so more of the collision will have enough energy to make the reaction happen
RATES OF REACTION: Why does increasing the concentration or pressure increase the rate of reaction?
• in a liquid there are more particles on the same volume of solvent • in a gas, the same number of particles occupy a smaller space • this makes the collisions between the reactant particles more frequent
RATES OF REACTION: Why does increasing surface area increase the rate of reacion?
• if a reactant is a solid, breaking it up into pieces increases its surface area to volume • for the same volume of solid, the particles around it have more area to work on - so there will be collisions more frequently
RATES OF REACTION: What is a catalyst?
a substance that speeds up a reaction, without being used up in the reaction itself (so its not part of the reaction equation)
RATES OF REACTION: - Different catalysts are needed for different reactions
RATES OF REACTION: How do catalysts work?
• by decreasing the activation energy needed for the reaction to occur • they do this by providing an alternative reaction pathway with a lower activation energy
RATES OF REACTION: What are enzymes?
biological catalysts - they catalyse reactions in living things
RATES OF REACTION - practical: What are the 3 ways to measure rate of reaction?
• precipitation and colour change • change in mass (usually gas given off) • the volume of gas given off
RATES OF REACTION - practical: What does turbidity mean?
the cloudiness of a solution