Chemistry Coursework- Planning Introduction In this piece of coursework I will attempt to design an experiment that will lead to a graphical procedure to determine the rate equation for the reaction between sodium thiosulphate and hydrochloric acid Scientific knowledge Before any chemical reaction occurs two or more molecules of the reactants must successfully collide together in the right orientation (the correct angle), the more collisions the faster the reaction rate. Concentration is just one of many factors which can affect this reaction rate and it is this factor which we will use to determine the rate equation of the reaction we will be monitoring. "For many reactions involving liquids or gases, increasing the concentration of the reactants increases the rate of reaction." (web) Using an acid as an example, the higher the concentration of the acid the more H+ ions are present thus there is a greater chance of a successful collision occurring. In our experiment we will be looking at what effect changing the concentration of both the sodium thiosulphate and the hydrochloric acid has upon the overall reaction rate, by plotting graphs based on this data we are then able to find the rate equation of the reaction.
''rate equations: equations giving the relationship between reaction rate and concentrations of reactants.' ' (web) Rate equations can tell us whether a reaction is 1 st, 2 nd or Zero order: 1 st order reactions -Reactions in which the rate varies with concentration of a single species, and the change in concentration is exponential, so that a plot of ln (concentration) vs. time is linear. The stoichiometric coefficient is 1. Radioactive decay is an example usually cited, but many electron transfer processes, and most enzyme mechanisms contain intermediate reactions that are first order. 2 nd order reactions- Reactions in which the rate varies with concentration of a single species, but the stoichiometric coefficient is 2. The rate varies with the reciprocal of the concentration, so that a plot of 1/ (concentration) vs.
time is linear. Alternatively they can be reactions in which the rate varies with the concentration of two substrates, each of which has a stoichiometric coefficient of 1. Zero order reactions-Many reactions in biochemistry appear to occur at a rate independent of substrate concentration. These are said to show zero-order behavior. To plot the graphs required to work out this rate equation we need to monitor the amount of product produced, in this case we will only be looking at the solid sulphur that forms when the two reactants are allowed to react. To work out the relative concentration of sulphur present we will look at the time it takes for a cross placed under the reacting vessel to become no longer visible.
The more sulphur produced, the more opaque the reacting vessel meaning less light passing through and decreasing visibility. Note. In this coursework [ ] will denote concentration Preliminary tests were carried out and the following results obtained.