Because the particles do not have to move around and just gather in one place where they react the activation energy is lowered.
Affectof surface area on rates of reaction
If a solid reactant or a solid catalyst is broken down into smaller pieces the rate of reaction will increase. The increase in reaction’s speed is because smaller pieces of same mass solid have a greater surface area compared to a larger piece of solid. Therefore, there is more chance that the reactant particles will hit the solid surface and react. The more collision that take place the faster the reaction.
The mass of the reactant is the same, but smaller pieces have a bigger surface area than the larger one. So more collision frequency and more collisions results into a faster reaction
The affectof light on rate of reaction
Increased light intensity increased the rate of some reactions; some reactions do not proceed without UV light. Light transfers energy to the reactant particles, so the collisions are more energetic.
The affectof stirring on rate of reaction
In rate experiments with solid and solution reactant, stirring the mixture is an important factor. The reactant concentration becomes much less near the solid, which leads to settle out at the bottom. Therefore, at the bottom the reaction slows down distorting the overall rate because the reactants are not evenly spread out.
The reaction is faster when stirred, as there are more collisions.
I studied the factors that would have an affecton the rate of reaction and so I will try to these factors constant so there is no affecton the rate of reaction. I will keep the temperature constant, use the same length of Magnesium to have same surface area, I will avoid stirring the reactants and not shine light on it.
Preliminary experiment
The aim of the preliminary experiment is to carry out investigation of different HCl concentration and rate of reaction with Magnesium. I will use acid concentrations 0.5M, 0.75M, 1.00M, 1.25M, 1.50M, 1.75M and 2.00M of volume 10cm3. I can’t do use higher than 2.00M of HCl concentration as it is dangerous to deal with. The length of Mg I will use is 5cm of average weight 0.085g.
The setup of apparatus is as following:
I timed the rate of reaction and measured the volume of Hydrogen produced.
The table of results
The preliminary experiment results that I should keep the following measurements constant.
- The lowest concentration of acid I will use is 0.75M, I would not use lower concentration than that because 0.50M took too long and I only have few lessons to finish the experiment in.
- The highest acid concentration I will use is 2.00M. I can’t use higher concentration as I will not be provided because of safety issues and also because the rate of reaction will be very fast to record the time and measure the volume of Hydrogen produced.
- The time intervals will be as following:
As I increase the concentration of acid, I will reduce the time intervals because the reaction will undergo faster
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I will use a 100cm3 measuring cylinder to collect the gas, because the range of hydrogen gas produced is 80 to 50.
- I will try and do the experiment in one day and same environment so there is no affectof different temperature on rate of reaction.
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The magnesium fully reacted in all the different HCl, this means 10cm3 of HCl is excess this means that Magnesium will fully react.
Apparatus and its uses
- Hydrochloric acid (concentrations 0.75,1.00,1.25,1.50,1.75,2.00 moles)
- Magnesium strip (0.085g, (4.95cm to 5.005 cm))
100cm3 to measure amount of Hydrogen produced
10cm3 to measure amount of HCl acid
- Ruler to measure length of Mg strip
- Stop watch to time the rate of reaction
- Trough of water (the method of collecting the gas is ‘under water’ as it does not react and I can collect enough gas through this method)
- Side arm test tube
- Delivery tube to deliver hydrogen gas from test tube to measuring cylinder
- Bung to stop hydrogen gas from escaping
- Clamp and clamp stand to the test tube and measuring in place
- Goggles for safety
- A table to record the results
The set up of apparatus is shown in method
Safety
- Wear goggles all the time
- Avoid touching test tube as reaction is exothermic and could b hot
- Avoid touching the Hydrochloric acid.
- Do not walk around with the acid
- Remove all other equipments from the table other than the apparatus mentioned above.
Method
- Place all the equipment mentioned in apparatus on a table, put our goggles on
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Place the 100cm3 measuring cylinder into the trough of water and fill it upside down so there is no air trapped in measuring cylinder. Use the clamp stand to hold the measuring cylinder upside down, make sure you can read the numbers on measuring cylinder.
- Connect the delivery tube with side arm tube. Use another clamp stand to hold the test tube over the trough of water. Place the delivery tube under the measuring cylinder so that no gas can escape.
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Starting with the lowest concentration of HCl, measure 10cm3 of HCl using the 10cm3 measuring cylinder and pour it in to the side arm test tube.
- Get a Magnesium strip of 5cm, twist it around to form a DNA shape (so it does not stick out or the acid in test tube) and deliver it into the side arm test tube. Close the bung on test tube so no gas can escape. You should have started the stop watch as you put the magnesium strip in to the acid.
- Depending on the acid concentration and time intervals record the volume of gas given off. Record the time it takes for the Magnesium to disappears
- Repeat steps 2 to 6 with same acid concentration until you achieve two results that are very close together
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Wash the side arm test tube and the 10cm3 measuring cylinder and dry them.
- Repeat steps 2 to 7 with a all the other acid concentration.
The diagram shows how to set up the apparatus
Have more than one person doing the experiment, because one student should watch the Magnesium until disappears, one student to time the reaction and another to record the data.
The table of records should have columns and fields…
Fair test
Through the following ways I will produce an accurate and fair result
- I measured the length of Magnesium to 5 cm to keep the surface area the same. I will use the same amount of Magnesium so there is no affect on the volume of Hydrogen produced.
- I will carry all my experiments in the same day and in the same room, so there is no interference from different temperature.
- I repeated my experiment more then once to get more accurate and reliable result.
- I washed and dried all equipments before using them again, so there is no interference from previous HCl concentration.
- I rolled the Magnesium strip into a helix shape so it completely sinks in HCl, if some of Mg surface is not in contact with HCl, this will affectthe rate of reaction.
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I will use exact 10cm3of HCl through out experiment
- I have removed the oxide layer from Magnesium so there is no affecton rate of reaction.
MgO + HCl MgCl2 + H2O
If oxide layer is not removed water is formed and solutions is diluted and less hydrogen is produced
- I will make sure there is no air trapped in measuring cylinder so there is no affecton volume of hydrogen produced.
- We had different people in our group doing different job, to achieve an accurate result, such as one person for timing, one person to put Magnesium strip and to close the bung quickly and one person for watching Magnesium disappear and the volume of hydrogen produced.
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I used 10cm3 of HCl so it is in excess and the Magnesium will fully react.
Tables of results
Concentration of Hydrochloric acid 2.00M
Concentration of Hydrochloric acid 1.75 M
Concentration of Hydrochloric acid 1.50 M
Concentration of Hydrochloric acid 1.25 M
Concentration of Hydrochloric acid 1.00 M
Concentration of Hydrochloric acid 0.75 M
Calculating the initial rate of reaction
The calculation is as following
Gradient = change in Y axis/change in X axis (cm3/s)
Gradient is 18/39 = 0.462 cm3/s (3 d.p)
Gradient is 10/8 = 1.250 cm3/s (3 d.p)
Gradient is 15.5/10 = 1.550 cm3/s (3 d.p)
Gradient is 17/6 = 2.833 cm3/s (3 d.p)
Gradient is 18/6 = 3.000 cm3/s (3 d.p)
Gradient is 45/10 = 4.500 cm3/s (3 d.p)
Conclusion
As I has predicted, that increasing the concentration of HCl will have such affect that the reaction will undergo faster. This happens because the higher the concentration of acid the more HCl molecules there are which increase in the number of collision with Magnesium leading to a faster reaction. Data I achieved from my experiment clearly show that the higher the concentration the faster the reaction.
Graph 1) “Average time taken for Mg to disappear at different concentration of HCl”
When the concentration of HCl is 0.75M the time taken for Magnesium to disappear is 1200 seconds, at 1.00M it is 390 seconds, at 1.25M it is 270 seconds the reaction is very faster at the end reaching only to 65 seconds at 2.00M of HCl.
The graph clearly shows the higher the concentration of HCl the less time taken is taken for Magnesium to disappear. At 0.75M there are very few HCl molecules so there are fewer collisions between Magnesium and HCl molecules, leading to a slower reaction. As the concentration of HCl increases the number of HCl molecules increases, while volume is the same, there are more HCl molecules so there are more collision between Magnesium and HCl molecules leading to a faster reaction. When concentration of HCl is 2.00M, it only takes 65 seconds for Mg to disappear.
There is some result in graph which does not fit the line of best fit. These result may have achieved because of the wrong recording or because the reaction is exothermic and produces heat. At a higher temperature the rate of reaction is faster because particles have more kinetic energy, the move faster and collide more often with enough energy ‘activation energy’. This is more likely to have affected my results.
Graph 2) “The average volume of hydrogen produced in different HCl concentration”
The line of best fit for 2.00M HCl, at time 0, no hydrogen is produced as the reaction starts after 10 seconds 35.7cm3 of hydrogen is produced, between 10 to 60 seconds the volume of hydrogen slows down reaching to 84cm3 after 65th second the reaction stops.
As the reaction starts there are lots of HCl molecules and lots of Magnesium molecules so there are lots of successful collisions and the rate of reaction is very high. As the time passes the number of HCl and Magnesium molecules decreases because they are reacting. Because there are fewer molecules left the number of collision decrease and this lowers the rate of reaction so less volume of Hydrogen gas is produced.
The same is the pattern with, 1.75M, 1.50M, 1.25M, 1.00M, and 0.75M. At the beginning the reaction is very fast because there are lots of both reactants and lots of successful collisions so reaction rate is very high. As time passes more and more molecules react and are being used, at the end very few reactants are left there are few collisions slower reaction so less hydrogen is produced until reactants finish and reaction stops. The higher the concentration of HCl is the steeper the line of best fit and the faster the rate of reaction.
I did not complete the result for 0.75M HCl on the graph; the reaction took very long time. At the end of reaction there were very few reactants left, between 600 to 1200 seconds only 7.5cm3of hydrogen gas was given off. This is because few particles lead to fewer collisions and so the reaction went on for very long time.
Graph 3) “The initial rate of reaction”
The line of best fit shows at 0.00M no reaction will take place, as the moles of HCl increases the rate of reaction increases. At 0.75M of HCl the rate of reaction is 0.462 cm3/s (3 d.p). As the concentration reaches 1.00M the rate of reaction is 1.250 cm3/s (3 d.p). There is very little increase in rate of reaction at 1.25M of HCl (1.550cm3/s (3d.p)), after that very high difference in rate of reaction between 1.50M, 1.75M, and 2.00M from 1.550 to 4.500cm3/s (3 d.p)
In 0.75M of HCl there are very few HCl molecules so very few collisions between reactant so the rate of reaction is very slow. As the mole of HCl is increased there are more molecules and hence more collision between the reactants leading to a faster reaction as a result at 2.00M the rate of reaction is 4.500 cm3/s (3 d.p).
There is some result in graph which does not fit the line of best fit. These anomalous results may have achieved because the reaction is exothermic and produces heat. At a higher temperature the rate of reaction is faster because particles have more kinetic energy, the move faster and collide more often with enough energy ‘activation energy’. This is more likely to have affected my results.
From this graph I can comment what the rate of reaction will be if the concentration acid in increased further. Following the line of best fit I predict the rate of reaction will be 5.250 cm3/s (3 d.p) when concentration of HCl is 2.25M and at 2.50M the rate of reaction will be 5.900cm3/s (3 d.p).
One major factor that must have affected my experiment is the reaction being exothermic. This reaction is exothermic, because it releases heat energy to surrounding. A reacting is exothermic when the energy released in break bonds is more than needed to make the new bonds and so the extra energy is given to surroundings. This affects the rate of reaction as it increase the temperature the reactants gain energy and collide more often with enough energy.
Volume of Hydrogen gas
The average volume of Hydrogen produced in my experiments is 84.62cm3. In theory the volume of gas I should have achieved when the average mass of Magnesium I have used is 0.085g is…
Mg + 2HCl MgCl2 + H2
One mole of any substance contains the same amount of particles, the Avogadro’s constant (6.022*1023) when one mole of Magnesium reacts one mole of Hydrogen is produced so this means they have the same number of particles.
Mole = mass/molar mass
Mole of Mg = 0.085/24 = 0.003541666667
The ratios is 1 mole of Magnesium produces 1 mole of Hydrogen
So… mole of H2 = Mg = 0.003541666667
At room temperature and pressure 1mole of any substance occupies 24000cm3.
To work out the volume of Hydrogen produced = mole * 24000
Moles of Hydrogen is 0.003541666667 * 24000 = 85cm3
The average volume of Hydrogen from my experiment is very close to the actual volume of gas I should have achieved. This shows my experiment was very accurate. The little difference is there because while collecting the gas some gas must have escaped while closing the bung or maybe some air was left in the measuring cylinder.
Evaluation
My investigation on rate of reaction was very successful. I produced very reliable and accurate results to support my prediction. The data I achieved is very reliant even though there are some anomalies; the rest of the data clearly shows a pattern, ‘the higher the concentration of acid and the faster the rate of reaction’. The odd results I have achieved, I think is because of the affectof temperature, as the reaction is exothermic and produces heat, also the experiment was carried at different times of the day. However the data from the experiment supported my prediction and conclusion.
The method I carried and apparatus I used were very easy and straight forward. The apparatus was easy to set and the method allowed to achieve a dependent data. There were some difficulties such as reading from the upside down cylinder. It was difficult to measure exact 10cm3 of HCl because always some acid was left behind in the measuring cylinder. The time intervals for 2.00M of HCl was longer for the volume of hydrogen produced.
Considering the above difficulties if I am to carry out this experiment again I will make the following changes:
- I will use a gas syringe to measure volume of Hydrogen as it is more accurate and easy to read from.
- I will use a pipette instead of measuring cylinder to measure the amount of HCl, this is more accurate equipment for measurement.
- I will try and carry out the experiment at closed possible temperature so there is no heat affect.
- I will use shorter time intervals for higher acid concentration as the reaction undergoes very fast.
- I will use a variety of different acid concentrations than I have used and I will repeat the experiment more often to get accurate and reliable results.
To study the affects of concentration on rate of reactions in more details I could use my method and apparatus to investigate the affect of concentration of HCl on different group 2 metals of the periodic table such as Beryllium, Calcium, and Strontium. I could study the rate of reaction of different metals and find the relation ship between the group 2 metals reactivity.
The group 2 metals become more reactive descending the group. This is because the outer most electrons that is lost in a reaction is further away from the nucleus going the group and so they are easier to remove because there is less attraction between the nucleus in the outer most electron the reaction will become more violent so I have to be careful. The reactions becomes more exothermic going down the group because the ionisation energy (the energy needed to remove the electrons) decrease so more energy is released in breaking the bonds than used in making new bonds.
X +2HCl XCl2 + H2
The apparatus I will use for this experiment is the same I have used before, except that will use a pipette and gas syringe instead of a measuring cylinder. Some of group 2 metals are very reactive so I have to be careful and I think I must use a very small amount of the metal. I will use a range of acid concentrations between 0.5M to 2.00M or 1.75M because some of the metal will be very reaction. I will use 10cm3 of HCl so it is excess and 0.5g of the metals of length 3cm. I will use very short time interval for collecting the gas, Magnesium is at the top of group so the other metals will be more reactive.
The method for this experiment will be the same as the one in my experiment except that I will use pipette and gas syringe instead go measuring cylinder.
The diagram shows how to set the apparatus.
Time intervals will as following
After experiment I will work out the reactivity of the metals and hopefully according to the prediction the graph should look like this.
Science coursework: Rates of reaction
Sharifullah Yaquby
