Aim Calculating the rate of reaction change with zinc powder and zinc pieces and calculating the enthalpy rate of copper sulphate

Aim
Calculating the rate of reaction change with zinc powder and zinc pieces and calculating the enthalpy rate of copper sulphate.
Abstract
The reaction rate practical is conducted with zinc powder and zinc pieces to allow participants a chance to see how long it takes for both to react with a copper sulphate solution, a thermometer is used to record an initial temperature and a stop clock used to determine how long the reaction takes. The results are recorded to allow calculations.
The enthalpy change for copper sulphate is calculated to allow knowledge of any possible energy change that would involve the transfer of energy to its surroundings, the symbol for an enthalpy change will be ?H and the units will be recorded in kilojoules per mole (KJmol¯¹).
Introduction
Sometimes when a chemical reaction expels energy or soaks up energy, the amount of change to the energy is nothing overall when such reactions take place. This means that the energy is neither destroyed or created, this is known as the law of conservation of energy. It is possible that the chemical reaction may change form, but ultimately the energy remains the same as before the reaction took place, and this is known that this is a true representation of chemical reactions. (Foundation, (2018)
When any system experiences any type of change, almost always there is an energy change that involves an energetic transfer between the surroundings and system. When this transfer happens, it is known as an enthalpy change and occurs at a constant pressure. Enthalpy change is measured in the units KJ mol¯¹ and has a symbol ?H. (Hill and Hunt, (Pg. 29, (2012)
Whenever an energy is given out to its surroundings it is known as an exothermic change. This type of change involves the energy leaving its system. The most obvious exothermic change is burning, another type of exothermic change is respiration, hot drinks used to treat various conditions are regarded as an exothermic reaction. (Hill and Hunt, (Pg. 29, (2012)
To break any type of bond there is energy required to do this. The energy within the bond is needed to break any particular type of chemical bond, although many types of bonds will have bond energy that is completely different. For any type of bond to break requires energy that is the same amount released when forming a bond. (English, (PG 210, (2011)
When the energy is less for bonds to break when new bonds is forming is called an exothermic reaction, and when the energy is more for bonds to break when new bonds is formed is called an endothermic reaction. (English, (PG 211, (2011)
When any type of energy is taken in it is known as an endothermic change. Some of these endothermic changes occur when melting happens and even more so with vaporisation, another type of endothermic change is that of photosynthesis. A diagram for enthalpy change shows when there is more energy in the system after the endothermic change, for any endothermic change it is positive with such energies being higher than any of the reactants. (Hill and Hunt, (Pg. 30, (2012)
Diagram showing exothermic and endothermic reactions

(Anon, 2018)
Within enthalpy there are various types, but the ones that are being concentrated on are standard enthalpy of formation, standard enthalpy of neutralisation, standard enthalpy of reaction and standard enthalpy of combustion. These four in particular have their own unique definitions and are as follows-
Standard enthalpy of formation- is when one mole of any given compound is formed via the standard state from the elements which is in their standard states which came from standard conditions. (Maginty A, (2018)
Standard enthalpy of combustion- is when any one mole is altogether burnt away with an excess amount of oxygen while under standard conditions. (Maginty A, (2018)
Standard enthalpy of neutralisation- this enthalpy change happens when any acid is neutralised by any alkali which produces one mole of water at a specific temperature. (Maginty A, (2018)
Standard enthalpy of a reaction- although it is not quite possible that enthalpy can itself be measure it is however possible to test new ideas which could help to determine an enthalpy change. By this method an equation is formed to help which is q=mc?T, where m is the surrounding experiencing temp change, c is the specific heat capacity, ?T is the change in temperature and q is energy change measured in KJ. (Maginty A, (2018)
Zinc powder is of a grey-blue colour which has no distinct smell and is insoluble. It is known to reach a boiling point of approx. 907°c and also has a melting point of approx. 419°c. it is labelled as flammable and if not handled correctly it may lead to spontaneous combustion. It is fairly stable with proper usage and stable if stored correctly. (Sciencing, (2018)
Zinc is a well-known metal that can be found within the crust of the earth, it also has a vast number of uses within industry and uses within biological terms. Within room temperature zinc is known to be fragile and of being of blue-white origin. Zinc is fundamental within galvanized steel to stop from rusting, it can be used in the marine industry as well. It is a moderate conductor but serves a good purpose within batteries, at approx. 212°c zinc will become ductile but as soon as the temperature becomes raised it will revert to becoming brittle. (The Balance, (2018)
Any chemical that has a reaction almost certainly has a reaction rate, this is to do with the change of concentration within the reactants if the concentration with any product changes. This type of reaction is measured with the units dm¯³s¯¹. There is however some factors that would help to influence the rates of reaction, these include-
. Reactant concentration
. The solid reactant surface area
. Any change in temperature
. If a catalyst is present (Revisionscience.com, 2018)

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An example of a graph showing rate of reaction with a catalyst

(Docbrown.info, 2018)
Whenever a reactive element is able to force out an element that is less reactive, then this what’s known as a displacement reaction. An example being that if chlorine where to be added to a potassium bromide solution, eventually the bromine will be replaced by chlorine which in turn will form potassium chloride. (GCSE Additional Science Complete Revision and Practice, (2007)
Enthalpy can and is used in the real world despite not many realising that it actually happens. Two real world examples of enthalpy are the compressors found in refrigerators and hand warmer that are used in cold conditions. But despite both giving results that are completely opposite they still obey the law of conservation of energy. When the refrigerator compressor converts chemicals into vapour, the will be absorbed thus creating an endothermic reaction. Within the handwarmer, iron oxidation occurs this in turn creates an exothermic reaction which means it releases the heat that is generated. But yet with the amount of energy that is in their systems, they still remain the same. (Reference, (2018)
Apparatus
2x 250ml polystyrene cups with lids
2x 250ml beakers
1x thermometer
2x weighing boats
2 DP mass balance
1x spatula
1x 25ml pipette
3g zinc powder
3g zinc pieces
1Mol dm¯³ Copper sulphate (25ml)
1x stopwatch

Method
The preparation for this practical started by collecting laboratory coats, nitrile gloves and safety goggles. For the practical itself the following equipment was collected to ensure the practical could take place, two polystyrene cups and lids, two 250ml beakers, stopwatch, mercury thermometer and a 25ml pipette.
Following on from this two weighing boats, a clean spatula and a mass balance was also collected, along with two containers each containing zinc powder and zinc pieces was also collected. The practical began with placing a dry polystyrene cup inside one of the 250ml glass beakers. A volumetric flask containing 1mol dm¯³ copper sulphate was collected to allow progression.
Exactly 25.0cm³ of 1mol dm¯³ copper sulphate solution was pipetted into the polystyrene cup, this was followed by placing the lid onto the cup and inserting a mercury thermometer into the cup, this was to allow the initial temperature to be recorded. Once this was achieved, 3g of zinc powder which was carefully weighed out on the mass balance while on a weighing boat and took back to the appropriate work station
The stopwatch was started when the 3g of zinc powder was gently poured into the polystyrene cup and mixed via the spatula or swirling. A time was recorded as to how long it took to reach the optimum temperature and was recorded in a table designed for such results.
The same steps was repeated again when using 3g of zinc pieces and timed exactly the same way as to how long it took to reach the optimum temperature, these results were also recorded into the appropriate table. Once both results where tabled, this then allowed the enthalpy calculations to begin.

Results
Table showing two compounds with max temperatures, temperature difference and time taken to achieve this
Compound Initial
temp °c Max
temp °c Temp difference °c Time taken
Zinc powder 24°c 48°c 24°c 56 secs
Zinc pieces 24°c 48°c 24°c 12min 31secs
Discussion
When the practical was taking place, it was noted from the results that the zinc powder had a faster reaction time than the zinc pieces, it was also noted that some heat could be felt from the polystyrene cups during the experiment from both practicals, this indicated early that this was an exothermic reaction.
When an exothermic reaction takes place, it will transfer the energy into the surroundings which result in some heat being transferred as well. There are some typical exothermic reactions and these are known to be combustion and neutralisation. As the reaction starts to gather pace it will undoubtedly transfer its energy, the energy change can be shown and measured in a simple way, this is done by the following ?H. (English, (2011)

Diagram showing the overall change within an exothermic reaction

(Docbrown.info, 2018)
From the table it was visible that the zinc powder reacted faster than the zinc pieces, the zinc powder took less than a minute whereas the zinc pieces was near 13mins, it was concluded that due to the zinc powder having a larger surface area than the zinc pieces allowed for the rate of reaction to be considerably faster than the pieces.
To increase the reaction rate of a substance can be increased by having a large surface area from a reactant that is a solid. To help this process, the substance being used can be either cut into pieces that are small or using a grinding method to turn it into a powder. When the surface area is increased, it will allow particles to be exposed to another reactant, it will also allow more collisions and ultimately increase the rate of reaction. (BBC.co.uk, (2018)

Diagram depicting a larger surface area with powder against a smaller surface area with small lumps (pieces)

(BBC.co.uk, (2018)
From the results gathered, the enthalpy change can be worked out for CuSO4 (copper sulphate). The calculations are as follows-
To start with the moles will have to be worked out, this involves converting cm³ to dm³
25cm³ – dm³= 25÷10÷10÷10=0.025dm³
Moles=0.025dm³ x 1.0moldm¯³
= 0.025moles of CuSO4
Now the enthalpy change can be worked out of copper sulphate, to see what heat has been exchanged into the surroundings by chemical reaction using the following equation q=mc?T
m= 25
c= 4.18
?T= 24° (48°-24°)
q= 25 x 4.18 x 24= 2508J ÷ 1000= 2.508KJ
2.508KJ/0.025m= 1mol/x
2.508KJ/0.025m= -100.32KJmol¯¹
?H= -100.32KJmol¯¹

The calculations for moles in zinc powder can now be worked out as well using the equation
q=mc?T
m= 25cm³
c= 4.18JK¯¹g¯¹
?T= 24° (48°c-24°c)
q= 25cm³ x 4.18JK¯¹g¯¹ x 24°c = 2508J ÷ 1000 = 2.508KJ
the RMM can now be worked out to further the calculation
RMM = Zinc=65
This is now divided by the amount used in grams
3/65=0.046mol
The kilojoules are now divided
2.508KJ/0.046mol= +54.52KJmol¯¹

the calculations for moles in zinc pieces can now be worked out as well using the equation
q=mc?T
m= 25cm³
c= 4.18JK¯¹g¯¹
?T= 24° (48°c-24°c)
q= 25cm³ x 4.18JK¯¹g¯¹ x 24°c = 2508J ÷ 1000 = 2.508KJ
the RMM can now be worked out to further the calculation
RMM = Zinc=65
This is now divided by the amount used in grams
3/65=0.046mol
The kilojoules are now divided
2.508KJ/0.046mol= +54.52KJmol¯¹

The equation for the practical involving zinc and copper sulphate is wrote down in the following way
Zn(s) + CuSO4(aq) —–? Cu(s) + ZnSO4(aq)
This equation clearly shows that a single displacement reaction has taken place, also a REDOX reaction has taken place as well. The displacement indicates that the zinc (Zn) is less reactive than copper (Cu), this in turn means that copper replace the zinc as the more reactive.
A redox reaction is one type of reaction in chemistry which is known to involve the transfer of electrons. This involves a number of molecules being oxidized or with ions gaining or in cases losing electrons. A redox reaction is important to all functions of life. (Chemistry LibreTexts, (2018)
A displacement reaction or in this case a single-displacement reaction, is a reaction when a type of element will react with another compound and inadvertently take the place of the other element with in that compound. (Study.com, (2018)
To make these results as reliable as possible, the results from a separate group was collected that participated in the same practical they will be known as group 1. It was established that the time achieved for the max temperatures was in fact extremely close but when both sets of temperatures where compared it showed that group 1 had achieved 8°c more. The enthalpy rates where also compared and this showed that group 1 had achieved ?H= -133.76KJmol¯¹, whereas these results where ?H= -100.32KJmol¯¹.
Although it could be argued that human errors could have played a significant part in the results it also shows the reliability and accuracy as it shows fairly similar trends with both sets of results.
Evaluation
As shown in the results and calculations, both enthalpy practicals proved to be reliable and fairly accurate. But with some recommendations that would possibly see some human errors ironed out, this could potentially leave such practical’s in the future lead to no errors and with 100% accuracy.
One such recommendation would be to use a digital thermometer instead of a mercury thermometer. Digital thermometers are able to give very accurate readings to the nearest tenth of the desired degree, although mercury thermometers have been used in practicals for decades sometimes reading the temperature can be particularly testing on the eye and can lead to misreading’s.
Although digital thermometers are extremely accurate, they do have a particular drawback this is that not everyone would remember to calibrate the thermometer, and the next user would find that their results could be compromised with false readings leading to inaccurate results.
Some possible human errors that could have possibly affected the rates of reactions could have been the way some participants where swirling the copper sulphate solutions with the zinc powder and pieces. Some participants where possibly swirling every few seconds, some possibly where possibly swirling throughout the experiments and somewhere maybe swirling at different rates.
One way that this could be implemented into future practicals is to if possible have a recommended guide to swirling patterns and rates of swirling, this would allow the users a guide to work off and could possibly cut down on any discrepancies on results.
Another possible source of human error could be the way some users where pipetting the solution into the polystyrene cups. It was noted that some users where removing the pipette filler, whereas some users where drawing the solution to the meniscus line and then releasing it into the cup. If a set rule was implemented for future experiments that only one way was acceptable to pipette, then this itself would be a huge benefactor on the way some results are recorded.
A possibility for future experiments to look at group sizes although these practicals where mainly made up of people, possibly doing it in groups of 3 could be of more benefit. The reason for this would be to give the best chance of achieving the most accurate results, with three people involved one user could be pipetting, one could be weighing the exact number of grams of zinc powder/pieces and another could be timing the rates of reactions. It would possibly be something to look into in future experiments.
Accuracy played a key part in this practical especially when using the digital balance and using the correct pipette. Although sometimes it can be forgotten to calibrate the digital balance which in turn can lead to a misleading weight or when pipetting sometimes the pipette filler has been damaged from previous practicals which won’t allow the correct amount of solution to be extracted for the practicals in question.
If possible, all pipette fillers should be checked for any malfunctions and a sign placed at the digital balance to remind users to calibrate before and after usage, as this would help participants to ensure all means of accuracy.
Conclusion
Both experiments proved to be successful as regards to finding out between the zinc powder and pieces which one reacted the fastest. It also gave the users an idea as to how an exothermic reaction takes and how to calculate the enthalpy rate of a copper solution, it gives a good idea when and how exothermic and endothermic reactions are applied in real life situations.