Rates of Reaction (2)
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Define rate of reaction.
how quickly a reaction happens
What equation allows you to calculate mean reaction rate?
mean rate of reaction = (quantity of reactant used OR quantity of product formed) / time
What are three different methods of calculating amount of product formed in a reaction?
• precipitation • change in mass • volume of gas given off
Describe an experiment to investigate the effect of surface area on rate of reaction. (10 steps)
• Use a measuring cylinder to measure 100ml of dilute hydrochloric acid and add it to a conical flask. • Weigh out 2g of marble chips using a mass balance. • Add the chips to the acid and quickly attach an empty gas syringe to the flask. • Start the stopwatch. • Take readings of the gas volume at regular intervals until the volume hasn’t changed for three readings in a row. • Put the results into a table • Plot a graph with time on the x-axis and volume of gas produced on the y-axis. • Use a pestle and mortar to lightly crush some more marble chips. • Repeat the experiment using these. • Repeat the experiment again with the same mass but of powdered chalk.
Describe an experiment to investigate the effects of temperature on rate of reaction. (7 steps)
• Start by measuring out 50ml of dilute sodium thiosulfate solution and 10ml of dilute hydrochloric acid. • Use a water bath to gently heat both solutions to the same desired temperature before you mix them. • Mix the solutions in a conical flask. • Place the flask on a piece of paper with a black cross drawn on it and start the stopwatch. • Watch the black cross through the solution and time how long it takes to disappear. • Record your results in a table. • Repeat the reaction a few times, heating the solution to a different temperature. Repeat the reaction three times at each temperature and calculate the mean time.
What are the three main factors that affect how quickly a reaction goes?
• temperature - higher temperature, faster reaction • concentration - higher concentration, faster reaction • surface area - larger surface area, faster reaction
What two things does collision theory say that the rate of reaction is dependent on?
• The collision frequency of reacting particles. (More collisions in a certain amount of time, increase the speed of reaction.) • The energy transferred during a collision. (Particles have to collide with enough energy for the collision to be successful.)
What is activation energy?
the minimum amount of energy that particles must have when they collide in order to react
Defne catalyst.
a substance which can speed up a reaction, without being chemically changed or used up in the reaction, and without changing the reaction process
How do catalysts work?
they decrease the activation energy needed for the reaction to occur they do this by providing an alternative reaction pathway with a lower activation energy
What are enzymes?
biological catalysts