Chapter 6: Rate and Extent of Chemical Change Flashcards
What is the formula for rate of reaction?
rate of reaction = product formed (g/mol/cm^3) / time (s)
How does the rate of reaction change during the reaction?
It decreases as the reactants are used up
How would you measure the rate of reaction at a certain point?
Gradient of tangent to the curve
How would you measure the volume of gas formed?
Attach a gas syringe to the reaction container
How would you measure the mass of the gas formed?
Block up the opening to the reaction container with cotton wool, and place it on a scale. Set the scale to 0, and the reading on the scale will decrease into the negatives as the gas escapes
What is activation energy?
The minimum energy that particles must have in order to react. If particles don’t have enough energy when they collide, nothing happens
How does increased temperature affect the rate of reaction?
It increases the rate of reaction because the particles have more energy when they collide. They also move faster and so collide more frequently. This increases the probability and frequency of successful collisions
Why do fridges prevent food from expiring?
The decreased temperature slows down the chemical reactions that cause food to go off
How does increased concentration affect the rate of reaction?
It increases the rate of reaction because the particles are closer together so collide successfully more frequently
How does increased pressure affect the rate of reaction?
It increases the rate of reaction because the particles are closer together so collide successfully more frequently (only works if one or more of the reactants are gases)
How does increasing the surface area of a solid affect the rate of reaction?
It increases the rate of reaction because there are more particles on the surface of the solid (which can react)
What is a catalyst?
A substance that speeds up a chemical reaction but does not get used up. It works by providing a different pathway for the reaction, with a lower activation energy
Name some examples of catalysts
Iron in the production of ammonia (Haber process)
Nickel in the production of margarine by reaction of vegetable oils with hydrogen
Enzymes are molecules that act as catalysts in biological systems
How is temperature different to other factors that affect reaction rates?
A small increase in temperature has a large impact on the rate of reaction: They are not proportional
What are reversible reactions?
Reactions in which the products can react to reform the reactants
