1.0.0- Introduction
1.0.1- Focus Question- If the mass of magnesium reacted with hydrochloric acid is changed will the temperature of the solution increase and the total mass decrease.
1.0.2- Hypothesis- If the mass of magnesium that is reacted with hydrochloric acid is changed the temperature of the solution will increase and the total mass will decrease.
1.0.3- Theory- The reaction between magnesium and hydrochloric reaction is written as follows, Mg(s)+ 2HCL (aq)—— (MgCl2(aq)+H2 (g) (Ng, 2008, pg 1). This reaction goes through two distinct changes that both have an effect on the energy change in the reaction.
Enthalpy refers to changes in energy in a compound (Assut, 2008, pg 1). Two distinct changes can occur. An endothermic change occurs when the energy being absorbed is grater then the energy being released whereas and exothermic change is when the energy being released is greater than the energy being absorbed. Energy is absorbed when bonds are broken and energy is released when they are formed (Newton, 2008, pg1).
Energy change cannot be directly measured. However energy change affects the physical force of heat.
Therefore a heat change is indicative of an energy change. If the heat increase in the solution the change will be exothermic and if the heat decreases the reaction will be endothermic. In respects to the formula Magnesium forms an ionic bond with chlorine to form the salt magnesium chloride. When this bond is formed energy is released in the form of an endothermic change, this energy drop would be quite small however because the bond is ionic and does not take much energy to create since magnesium and chorine bond easily.
However the second change is that hydrogen breaks off from chlorine in the hydrochloric acid and hydrogen is released as a gas.
The breaking of bonds would absorb energy therefore forming an exothermic reaction. Hydrogen and chorine however form a very strong covalent bond. Covalent bonds form between atoms with similar electronegative forces and are there for take a lot of energy to break ( Anissimov, 2008, pg 1) Since the endothermic change is weak and the exothermic change is strong it can be predicted that the overall change will be exothermic and therefore the solution will heat up. Temperature change in a chemical reaction can be measured with a device known as a calorimeter. A calorimeter measures the heat of the solution before the reaction has occurred and then again after the reactant has been added (Whel, 2008, pg 1). These two values can be mathematically manipulated to find the relative change in temperature.
If two of the same substance have different masses it means there is more of the one substance. In a mass of a substance there is a certain amount of material that can be reacted. By increasing mass the amount of substance that may be reacted increases. Therefore if mass increased the amount that of substance reacted will increase as well providing there is enough of the reactant. This will in turn increase the energy change. Also if more of the substance reacts with the reactant more of the reactant will be used up. This means that if the magnesium is increased there will be more reaction with hydrochloric acid; this means that more hydrogen will be released as gas and the total mass of the solution will decrease. Henceforth the change in heat should be greater if their entire solution is lighter as more of the hydrochloric acid has been reacted and hydrogen lost as a gas.
How the reaction works (Figure 1)
Mg(s)+ 2HCL (aq)—— (MgCl2(aq)+H2 (g)
1.1.0- Controlling variables
1.1.1- Variables (Table 1)
Variable
Type of variable
Method for control
Mass of magnesium
Independent
Mass will change for each sample, sample range will be 2g, 4g, 6g, 8g and 10g
Heat change
Dependent
This will be calculated by subtracting the final heat of the solution by the initial heat of the solution. The data will be gathered by using a calorimeter
Change in mass in solution
Dependent
This will be calculated by measuring the weight of the solution and subtracting the weight of the calorimeter and the magnesium. The original mass not including calorimeter and the magnesium will then be subtracted by this value to mind the change of mass in the solution.
Initial temperature
Controlled
The temperature of the solution will be heated to 25c and the reaction started immediately.
External temperature
Controlled
The room temperature will be controlled at 24c
Volume of hydrochloric acid
Controlled
The volume of hydrochloric acid will be 40mls per sample.
Measuring apparatus
Controlled
A 50ml calorimeter with electronic thermometer and a scale with milligram accuracy.
Time of experiment
Controlled
The experiment will be ended when reaction is fully complete and reaction will be given 10 seconds to calibrate before results are taken
Replications
Controlled
Standard 5 replications of each sample will be performed.
1.1.2- Control used in comparison- The reacted samples will be compared against hydrochloric acid with no magnesium that is also 25 degrees Celsius. Since the temperature remains constant there should be no energy or mass change, this would mean that on a graph this would represent a straight line which others samples with energy changes (heat changes) could be compared to.
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Bibliography
Ng, H.N, 2008, Acid reactions, Vat.Gov.Un, Accessed 21/08/09, http://vat.maharashtra.gov.in/communicationcenter/QueryAnswerSubjectwise.php?start=3090&subId=0000000007.
Asset, M.A, 2008, Chemical Enthalpy, Nasa.gov, Accessed 21/08/09, http://www.grc.nasa.gov/WWW/K-12/airplane/enthalpy.html
Newton, R.N, 2008, Energetics and bonding, Unknown sponsor, Accessed 21/08/09, http://www.webchem.net/notes/how_far/enthalpy/enthalpy_diagrams.htm
Anissimov, T.A, 2007 Chemical bonding, Simon Frasier University, Accessed 21/08/09, http://www.chem1.com/acad/webtext/chembond/
Whel, L.W, 2006, Calorimeters, Stanford University, Accessed 21/08/09, http://www2.slac.stanford.edu/vvc/detectors/calorimeters.html
Acknowledgments
The procedure of this experiment is a adaption of a previous class experiment. The source of the procedure is unknown, so thanks to Miss Crook for the inspirations for this design.
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