The manipulated variable in this experiment is the temperature of the water bath. The manipulated variable affects the responding variable which is the time taken for the potassium permanganate to decolourize. The potassium permanganate decolourizes changes from purple colour to colourless when oxalic acid is added into the potassium permanganate.

This is a redox equation. The ion permanganate (purple) is reduced to ion manganese (II) which is colourless.

H2C2O4 ---> 2 CO2(g) + 2 H+(aq) + 2 e- (MnO4)-(aq) + 8 H+(aq) + 5 e- ----> Mn2+(aq) + 4 H2O(l) 

5 H2C2O4 ---> 10 CO2(g) + 10 H+(aq) + 10 e- 2 (MnO4)-(aq) + 16 H+(aq) + 10 e- ----> 2 Mn2+(aq) + 8 H2O(l) --------------------------------------... 5 H2C2O4 + 2 (MnO4)-(aq) + 6 H+(aq) ----> 10 CO2(g) + 2 Mn2+(aq) + 8 H2O(l)

The activation energy, Ea is defined as the minimum amount of energy required to initiate a chemical reaction. If the barrier is low, Ea is low, the energy required is low, high proportion of the reactant molecules may have sufficient energy to react, thus the reaction will be fast. For this experiment, presence of h202 as the catalyst was used to lower the activation energy. When the activation energy is lowered, more molecules could collide with one another increasing the frequency of effective collision thus speeding up the rate of reaction for the decolourization of potassium permanganate.

Exothermic reaction

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An exothermic reaction is a reaction that transfers energy to surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter.  It has a negative ΔH by convention, because the enthalpy of the products is lower than the enthalpy of the reactants of the system.

Endothermic reaction

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Endothermic reactions are reactions that take in energy from the surroundings. The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. A system of reactants that absorbs heat from the surroundings in an endothermic reaction has a positive ΔH, because the enthalpy of the products is higher than the enthalpy of the reactants of the system ( “ Exothermic vs. Endothermic “ n.d.).

There are a few factors affecting the rate of reaction. One of it is the size of reactant on the rate of reaction. Chemical reactions are faster when the same mass of solid reactants are broken into smaller pieces. The smaller pieces of a solid reactant have a larger total surface area exposed for collision. Thus, more collisions occur. The possibility for effective collisions increases. Hence, the frequency of effective collision increases and so does the rate of reaction. Other than that, the concentration of solution affects the rate of reaction. The rate of reaction is higher with a higher concentration of solution of the same volume. At a higher concentration, there are more particles per unit volume to the solution. The particles occupy a smaller space and are closer to each other. There is a higher chance of particles colliding with each other. The constant collision of particles increases the frequency of effective collision and thus the rate of

reaction is too, increase. Besides that, the temperature of the solution has effect on the rate of reaction. A higher temperature increases the rate of reaction. When the temperature increases, the reacting particles move about faster as their kinetic energy increases. Moving at high speeds, the reacting particles have a better chance of colliding with each other which will increase the frequency of effective collision and so does the rate of reaction. Pressure also affects the rate of reaction. The rate of a gaseous reaction increases at a higher pressure. Pressure however, has very little effect on reactions involving solids and liquids. At a higher temperature, the gas reactant is compressed. Thus, the number of molecules per unit volume of gas increases and the molecules are closer together. They collide more frequently. The more collisions there are, the higher the probability of collision being effective. The frequency of effective collisions increases and so does the rate of reaction. Catalyst too, has effect on the rate of reaction. The rate of reaction increases with the presence of a catalyst. A catalyst speeds up chemical reactions by providing an alternative path of reaction which has a lower activation energy. Thus, the reacting particles need less energy to overcome the lower activation energy of the catalyzed reaction. Less energy is required for particles to collide effectively and more collisions become effective. This increases the frequency of effective collisions, hence the rate of reaction also increases (Tan, 2007).

Arrhenius equation is a simple but accurate formula for the temperature dependence of the reaction are constant.

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According to the equation above,

T represents temperature (K) ; Ea represents activation energy ; the R gives us a value of 8.31x…..; A is the frequency factor (nkdnk) and k is the rate constant. However, the equation needs to be derived to find the activation energy :

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There are a few precautionary steps that has to be aware when doing the experiment. Firstly, the reactants should not be shaken after it is being added together because it will speed up the time taken to decolourise the potassium permanganate. Other than that, the temperature of both solutions which are acidified potassium permanganate and oxalic acid must be the same before adding it together.

Concusion:

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http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Le_Chatelier's_Principle/Effect_Of_Temperature_On_Equilibrium_Composition/Exothermic_Versus_Endothermic_And_