Reaction Rate Formula
The rate of chemical reactions is not just a theory, but can be formulated mathematically to facilitate learning. In chemical reactions: A → B, the rate at which substance A becomes the substance B is determined by the amount of substance A reacting or the amount of substance B formed per unit time. When the reagent (A) decreases, the reaction product (B) will increase. Consider the diagram of changes in the concentration of reactants and reaction results in Figure 3.
Diagram of changes in reactant concentration and reaction results.
Based on the picture, we can define the formula rate as:
a. reduced number of reactants (reactant concentration) per unit time, or, with r = reaction rate, - d [R] = reduced reactants (reactants), and dt = change in time. For reactions: A → B, the rate at which substance A decreases is:
b. increasing number of products (product concentration) per unit time, or, with + Δ [P] = increasing product concentration (reaction product). For reactions: A → B, the rate at which substance B increases is:
How for more complex reactions, such as: pA + qB → rC.
For this reaction, then:
In this comparison, the + or - sign does not need to be written because it only shows the nature of the change in concentration. Because the prices of each dt are the same, the ratio of reaction rates is in accordance with the ratio of concentrations. On the other hand, the concentration is directly proportional to the mole and also directly proportional to the reaction coefficient, so that the ratio of the reaction rate matches the ratio of the reaction coefficient. The comparison can be written as follows.
DISCUSSION
In practice this time an experiment has been carried out on the rate of reaction. There are four factors that affect the reaction rate including concentration, temperature, surface area, and catalyst.
In the first experiment, it was observed that the effect of concentration on the reaction rate was carried out by reacting the magnesium band (Mg) with HCl whose concentration was different. in tube 1 there is 0.5M HCl, in tube 2 there is 1M HCl, in tube 3 there is 2M HCl, and in tube 4 there is 3M HCl. in tube 1 the reaction rate runs very slowly at 234s, in the second tube the reaction rate goes rather quickly which is 104s, in tube 3 the reaction rate goes fast which is 28s, and in tube 4 the reaction rate goes fast which is 11s.
It has been proven that the higher the concentration of HCL, the faster the reaction rate goes. this proves that concentration affects the rate of reaction. if the concentration of a substance is greater then the reaction rate is faster and vice versa the smaller the concentration of a substance the reaction rate will run slowly. a solution with high concentrations will be more concentrated and contain denser particles so that they will collide more frequently. Based on experiments that have been carried out, it can be seen that our observations are in accordance with the theory of the reaction rate ie the greater the concentration of a solution of eating the faster the reaction rate occurs.
In the second experiment, the effect of temperature on the reaction rate was carried out. Mixing HCl with Na2S2O3 which is different at room temperature 29oC and temperature after heating that is at temperature (40, 50, 60) oC. when Na2S2O3 at 29 oC, it takes a long time until the color of the solution is milky white, that is 170s. when the temperature is raised to 40 oC the time needed is shorter, 122s. then the temperature is raised again to 50 oC the time required is even shorter, that is 107s. and finally we raise the temperature to 60 oC the time required is very short which is 52s.
this happens because the temperature plays a role in influencing the rate of reaction when the temperature which takes place in a reaction that takes place is increased, it causes the particles to move more actively, so that collisions that occur more frequently, it causes the reaction rate faster. conversely when the temperature is lowered, the particles are less active, so the reaction rate is slower. this is in accordance with the theory of reaction rates, namely the higher the temperature, the faster the reaction rate.
In the third experiment, an experiment affected the surface area on the reaction rate. based on experiments, 1 gram of crushed marble which was reacted with 5ml of HCl 2M reacted faster than a lump of marble of 1 gram reacted with 5ml of HCl 2M. in theory, the solid powder usually produces a faster reaction than a lump of solid mass of the same mass, because the powder solid has a larger surface area.
a substance will react only if the substance is mixed and collisions occur. the collision occurs between collisions of the surface area of the touch fields of each molecule. the smaller the particle size of a substance the more surface area of a substance. so, the smaller the particle size of the substance, the reaction will take place quickly. this is in accordance with the concept of the rate of reaction ie the greater the surface area, the faster the reaction rate.
In the last experiment the observation of the catalyst in the reaction rate. kalis is a substance that accelerates the reaction rate at a certain temperature, without undergoing changes in the reaction itself. a catalyst plays a role in the reaction but not as a reactant or product. in our experiment we used two different catalysts, namely nac and FeCl3. used three test tubes, the first tube containing 5ml H2O2 used as a control that is not treated anything. in the second tube which is 5ml H2O2 and 4 drops of nacl are added then a large amount of bubbles is formed and does not change color.
in the third tube containing 5ml H2O2 which then added 4 drops of FeCl3 the reaction occurs slowly, initially two layers are formed which are dark brown and clear and then smoke comes out and evaporates, the solution boils and the surface of the test tube feels hot, the color of the solution begins to mix and formed one color that is light brown. From the observations, it can be seen that the catalyst which is suitable with H2O2 is FeCl3. this can occur because of the nature of the catalyst like an enzyme, which only works on certain compounds. our observations are in accordance with the concept of the reaction rate, ie the catalyst can affect the reaction rate.