Factors that affects the rate of chemical reaction?

Onyi LEUNG Chemistry Coursework-Factors that affect the rates of chemical reaction? 10/05/2007

Introduction: The rate of chemical reaction is speed up by catalyst. Catalyst is the general term for any chemical that speed up chemical reaction. It can either be organic or inorganic. The one we’re focusing in this experiment is Catalyst in its organic form. Catalysts in its organic form are mostly to form enzymes. Enzymes are mainly consisting of polymer of amino acids design like the Chemical from the Catalysts, to speed up the metabolism of living things. Currently there’re more than 700 different kinds of enzymes being identified. They’re design to carry out different reaction. The main types are Hydrolytic, oxidizing and reducing. Hydrolytic enzymes broke down compounds with water molecule into simpler compounds, by reacting with the water molecules. Oxidizing (also call oxides), accelerate oxidization rates. Reducing enzymes accelerate the process of removing oxygen. Except for these 3 main types, there’re different types of enzymes each containing different chemical to catalyse different types of reaction. An enzyme is named by adding ase to the substrate that they’re going to react with. For example the enzyme that speeds up urea decomposition is call urease.

Enzymes are made up of multiple strands of polypeptides, which speed up chemical reaction. In its globular view under a microscope. It unstrands, folds, attracts amino acids to form active sites, and bind with the substrate that it is going to react with. The chemical reaction fails to happen if the substance of the substrate fails to match and fit with the shape of the enzymes. This protects the enzymes from involving from the wrong reaction. The enzymes are not affected by the reaction. When a product is being produced and release, it can be involve in another reaction, and bind with another substrate.

As the 1823 chemist Jöns Jakob Berzelius, who discovered enzymes suggested enzymes have a typical properties of being a catalyst speeding up a reaction, without being consumed in the process. There’re different types of enzymes, each has their own capability of carrying out different types if reaction, take pepsin found and release in stomach and trypsin found and release in pancreas use for digesting meat involve in different types of reaction, while other is more specific, for example urease, it can only carry out one process of decomposition of urea. There’re still many types of enzymes, that involve in many biological process, such as making the heart beats, expanding and contracting the lungs, facilitate the process of turning nutrient into various substance that is use for tissue building, making new blood cells and convert chemical energy to make muscle move. The two enzymes trypsin and pepsin mention above also have the peculiar properties of carrying out the process autocatalysis. This process is carried out because the enzymes need to reproduce itself, by reacting with a stable precursor call zymogen or proenzyme.

Each enzyme is selectively specific, with the substance that it’s going to react with, and the temperature which is the most optimum for it. Although an increase of temperature may accelerate reaction. But in the case of enzymes, when the temperature is increase and beyond its optimum temperature, it’ll start to denature and die. The activities of the enzymes depends on its amino acids sequences and its tertiary structure (Its three dimensional shape in the form of macromolecule.) Most enzymes need another ions and molecules, call co-factor, to enable them to function.

Finally enzymes do not attack living cells, because of cell membrane disallowing the enzymes to enter the cells. But as the cells die it cell membrane dysfunction and become permeable. It enters and breaks down all the proteins with in the cells. Unless the cells contain enzyme inhibitors, which prevents the substrate from binding with the enzymes and form reaction. For example in legumes. They contain enzymes inhibitor which blocks the enzymes trypsin to react with the protein in pulse. This is why people fluctuate in their colon, after ...

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Aims: After researching the details on enzymes above, I can now concentrate more on the enzymes I’m investigating in this investigation catalase. As the name suggest, Cata in Greek means to break down apart. Its function is to bind with Hydrogen peroxide, and break it down apart. Hydrogen Peroxide is a waste product from the cells. So the enzymes Catalase must break it down and make it decompose out of the body more quickly, before it is harmful to the cells. The formula for this chemical reaction is stated below.

2H2O2 2H2O + 2O2

From the toxic waste mixture of Oxygen and water. It is separated into oxygen and water, which the body can discompose safely and quickly.

In this experiment we’re going to use potatoes to provide the enzymes Catalase, to break down the Hydrogen Peroxide. At the same time observes my select point to investigate, seeing that does the rate of reaction differ, if I change the temperature.

Preliminary work: Before I have drawn up plan for my experiment. I need to make sure the results will be perfect. By deciding what’s the best amount of potatoes discs for the actual experiment. I’m going to use the same experiment latter on the actual experiment. But first I need to find out the ideal amount of potatoes disc that I’m going to use in the experiment, by timing using a timer to time how long it take for each amount of potatoes to produce a reaction with the Hydrogen Peroxide. I have taken 6 reading in total and the results illustrates below shown the more potatoes discs, the quicker the reaction. So I’m going to use the maximum amount of potatoes in my reading in my actual experiment of varying the temperature.

Apparatus: I’ve decided to use the following equipment for my investigation.

Bunsen burner
Fire proof mat
Beaker
Measuring cylinder
2cm3 of Hydrogen Peroxide in the Beaker
Stopwatch
Thermometer
12 pieces of potatoes each cut into 1cm 3 circular discs.
Borer
Tong and Manometer to measure amount of Oxygen produce, by measuring the pressure.

Fig 1 listed below is a hand drawn diagram of the list of the apparatus mention above, that I’ll use in the experiment.

Figure 1

Method: At first, I need to divide the potatoes into 12 circular discs, from 1 whole potato, using a borer, each need to be 1 cm3, and then I’m going to put the potatoes in the beaker, with 20cm3 of Hydrogen Peroxide, measure using a measuring cylinder. Then I’m going to start the measuring of the pressure of oxygen, and timing, when it is at room temperature, which I measure using the thermometer which is 24oC. The potatoes discs in the Hydrogen Peroxide are put in there for the same amount of time, starting from the first measured room temperature of 24oC, its temperature increase by 10oC after each measurement. Time will not affect my experiment; my only variable, I think is the temperature, increase by 10oC each time. As soon as I put the manometer over the beaker, I’ll start the stopwatch. Measuring the time, the manometer to measure 5cm3 of oxygen. I’ll repeat the experiment 3 times to find out the mean and ensure accuracy. The procedure, involves the following temperature: 24oC, 30oC, 40oC, 50oC, 60oC, 70oC. I’ve evolved this plan from the preliminary work that I did, in which a number of the procedures and variables are demonstrated. The key variables are stated below.

Key variables:

The effect of heat on temperature
Time for the oxygen to reach 5cm3
Concentration of the enzymes to the substrate Hydrogen Peroxide
The surface area of the potatoes

I’m going to vary the temperature, and control other variable. I should only alternate the temperature, because this is my main variable and also I should ensure other variable the same, to ensure a fair test. To make sure the other variable the same. I need to follow strict implement towards the instruction given in the method section in every experiment taken. And finally to make sure the amount of Hydrogen Peroxide accurate, I need to measure it using a measuring cylinder. All of this can ensure me the variable are constant through out the experiment.

Safety Precaution: I would need to be careful when using Hydrogen Peroxide, because it is corrosive. I can protect myself by wearing a goggles. Lastly I need to be aware that Hydrogen Peroxide is a bleaching agent, because the school that provide laboratory coat and gloves, I need to be very careful to prevent spillage, in the process of pouring Hydrogen Peroxide.

Hypothesis: My prediction is supported by the kinetic theory, if I apply twice much heat, there’ll be twice as much particle vibration, and therefore the reaction will happen twice quicker. It is also supported by the collision theory. If I apply twice the heat, there’ll be twice as much collision; therefore the reaction will happen twice quicker. This only applies to the enzymes optimum temperature. After it is over the optimum temperature. The enzymes start to denature and dies.

Prediction: I think that the enzymes will work best at its optimum temperature 40-45oC. I think the reason for this prediction is because; the enzymes had an optimum temperature range of 40oC to 45oC, outside this range, the enzymes became inactive. I think this occurs because as the temperature change, the level of energy also change, affecting the force of the particle, decrease or increase, according to the temperature hot or cold. This will affect the macromolecular bond of the enzymes. It’ll either have not enough energy to bond together, or too much energy until eventually the bond is break. And because the force disturbed and altered the structure of the molecule. The site of the active site alters, and disables the enzymes to function, because the displacement of the active sites, stopping the substrates to binds and react with the enzymes. Take the human body as an example. As in the laboratory. Most enzymes shut down or even denature, beyond certain temperature. This can happen if the body temperature is too low or too high.

Referring to the collision theory, as the temperature increase, the rate of reaction also increase. How ever the structure of the amino acids which made up the enzymes also starts to lose its stability, due to the thermal energy. Reaction is the rate is the speed at which the substrate and enzymes react and proceeds towards equilibrium. For an enzyme catalysed reaction, the rate of reaction, refer to the amount of product, produce per minutes. The reaction rate depends on the energy level between the process of reaction and the products. The reactants are activated by adding energy, and descend the same level of energy to the product. This is known as the equilibrium, because the force of the energy in the product is balance and the reaction is finished. Enzymes accelerate the reaction. And Catalyst decreases the energy barrier between the reactants and products, making the reaction between the substrate and enzymes happen quicker.

Chemical reactions are speeded up as the temperature rose. This is due to more kinetic energy are being posses by reacting molecule, more molecule are becoming more active and involve in the reaction. Since enzymes are biological catalysts, enzymes reaction also tends to go faster, as temperature increase. How ever if the temperature is raise further, until it reach over the optimum. The vibration between the amino acid molecule in the enzymes and the water in living cells vibrates so great, that the vibrations disrupt and alter the structure of the enzymes. Until it denatures and die. Therefore heating up the temperature has more negative effects than positive. So my prediction in the experiment is that the enzymes will start to denature and dysfunction after 40oC, and my second prediction is as temperature increase, reaction rate will speed up by 50%, as kinetic theory said Kinetic theory said, if I apply twice much heat, the particle will vibrate twice quicker, therefore the reaction will happen twice quicker, but keeping in mind that enzymes will denature after 45oC

I’ve drawn a graph to predict the final results in figure 2.

Figure 2

Obtaining of results

Table of results:

Figure 3

Analysis:

Analysis of results:

Figure 3 is a graph showing the illustrated results of the table. It’s able to back up my results. You can see that where the enzymes are most active and where it starts to denature. I’ve found out that as the temperature increase in the beginning, so did the enzymes activities. The time for the Hydrogen peroxide to break down decrease, as illustrates in the Y axis, it take less time to collect 5 cm3 of Oxygen. But until it reach 60oC it start to denature and the line of the graph become steeper. These show that starting from this point. The time of reaction start to prolong, because of denaturation. As the enzymes become more denature, the time of reaction, become more and more slower, until it eventually cease. As I predicted the optimum temperature is 40-45oC, this is where most enzymes reaction takes place, and where the most collision takes place between the enzymes and the substrate.

The rate of reaction was higher, when the temperature is higher (up to 40 degrees). So is the energy level of the enzyme and the substrate molecule. They posses more kinetic energy to collide, therefore more reaction takes place. This also means that the rates increase, because more oxygen is produce at shorter time. The enzymes denature at around 60 Celsius, the bond vibrates with the water in living cells more violently, until it reach a point, where the bond is completely broken, because of the violent vibration, using the kinetic energy. And because the bond of the amino acid in the enzymes is damaged, this means that the site of the active site is permanently damaged. The enzymes is completely denature and die and no longer to form an enzyme-substrate complex, because its active sites is permanently damaged.

The results was supporting my prediction, the results at the lower end of the temperature are slower, because they posses less kinetic energy, to collide. The optimum temperature was nearly the same, instead of 40 Celsius being the optimum temperature; the optimum temperature is 45 Celsius. The temperature at which the enzymes denature is nearly the same temperature as 60oC, instead of 70oC as I predicted.

Evaluation: Although I conduct the experiment as accurately as I could. There’re still number of minor mistakes in the method that I used. Firstly I have a slight delay on starting the stopwatch. Because I need to put the 12 discs of potatoes, measure the Hydrogen Peroxide, collect the manometer to the beaker, and start the stopwatch at the same time all on my own. I also think that I should use the same potatoes in the whole experiment, but as we’re in the class sharing potatoes, it is impossible to follow the same potatoes, the potatoes will eventually be use up, before I need it by the class. To remove the problems and make the results more accurate. I could get a partner to help me carry out the experiment simultaneously. And about the potatoes, if I can do the experiment on my own, I could use the same potatoes, because, depending on how fresh the potatoes, the amount of enzymes do vary, so it’s better to use a very fresh potatoes and to prove that the enzymes content is the same, I need to cut up the same potatoes. I would also weight each pieces of potatoes to measure the weight, because at the moment, I only measure the size, if I measure the weight, the results will become more accurate. Finally I can make the scales of the measurement much smaller, instead of increasing the scale by 10, I could try increasing the scale by 5, and the results can be more accurate and precise.

The evidences that I collected is sufficient enough to support the conclusion. I have come about the value for the optimum and denature temperature, because I conduct my experiment as accurately as I could. The next time I did the same investigation. I need to make sure that every element in the method section is well considered, to prevent any possible mistakes in the results. Making the figure more accurate and reliable.

Glossary: I’ve learnt couples of new words in this investigation, mainly in the Introduction section, because there is where I done most of my reading and research. Below is their definition.

Substrate: A general term for any biochemical that binds with enzymes, to form reactants and react to form a product.

Catalyst: Any chemical that speed up chemical reaction, either organic or inorganic.

Enzymes: An organic catalyst, which is made up of strands of polypeptide strands. It unstrands, folds, and attracts amino acid to form active site and finally binds with substrates molecule to form reactants, to carry out chemical reaction.

Precursor: A chemical compounds that lead to a stable product in a series of connected reaction.

Zymogen: Is a stable precursor of an enzyme. It is secreted by living cells, and is activated by acids, another enzyme, or other catalytic mean to reproduce an enzyme.

Co-factor: A factor that an enzymes needs, such as an ion and molecules, to activate it.