Determination of thermodynamic values allows for analysis of what makes a reaction spontaneous. In this experiment, the equilibrium constant of the crystallization of potassium nitrate as it ionized in water was found and used to determine enthalpy, entropy, and Gibb’s Free Energy of a reaction. The variables were found by by graphing the solubility of potassium nitrate as a function of time and by utilizing relationships based on the van’t Hoff equation. Based on the determined Ksp of 43.4 the average Gibb’s Free Energy over on six trials was -8.4834 kJ/mol with a 510 % error. Relations based on the graph of ln(k) vs. 1/T(K) showed the enthalpy of the reaction to be +34.78 kJ/mol yielding a 2.30% error, and showed the entropy to be +137.4 …show more content…
In a given reaction, the total amount energy in a reaction that can be used to do work is expressed as ∆G, or Gibb’s Free Energy. A negative value would indicate energy is produced in the reaction and available to the surroundings. This would create a spontaneous reaction as the disorder of the universe would increase.2 One important factor in determining the Gibb’s Free Energy of a reaction is the equilibrium constant.
This experiment analyzes the following reversible reaction of potassium nitrate dissolving into potassium and nitrate ions. Reversible reactions reach a specific equilibrium where the forward and reverse reactions are occurring at an equal rate causing the ratio of products to reactants to appear constant. The formula for the equilibrium constant is written
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In the above reaction, a larger K value would indicate higher solubility as more ions are present in solution. Gibbs and the equilibrium constant are related based on the equation, ΔG° = -RT ln K.
As K gets larger Gibb’s becomes more negative showing increased spontaneity.1 The values that determine the Gibb’s Free Energy value are enthalpy and entropy. A relationship can be seen based on the Gibbs-Helmholtz equation where:
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The entropy (∆S) is the measure of a given reaction’s disorder. If the reaction moves forward and becomes more disordered, it is considered to have a positive entropy. In the ionization of potassium nitrate, the disorder of the reactants, solid, is less than the disorder of the products, aqueous. The enthalpy of a reaction (∆H) represents the energy difference between the potassium nitrate salt and its ions. A positive ∆H indicates the reaction is endothermic and absorbs heat to create products. Adding more heat to a reaction with a positive enthalpy would cause the reaction to shift right, increasing spontaneity and decreasing the Gibbs free
If the relative amount of reactants is altered, then the limiting reactant may change accordingly. For example, a balanced chemical equation of a certain reaction specifies that an equal number of moles of two substances A and B is required. If there are more moles of B than of A, then A is the limiting reactant because it is completely consumed when the reaction stops and there is an excess of B left over. Increasing the amount of A until there are more moles of A than of B, however, will cause B to become the limiting reactant because the complete consumption of B, not A, forces the reaction to cease.
As the temperature increases, the movements of molecules also increase. This is the kinetic theory. When the temperature is increased the particles gain more energy and therefore move around faster. This gives the particles more of a chance with other particles and with more force.
== = Hess’s law of heat summation states that the value of DH for a reaction is the same whether it occurs directly or as a series of steps. This principle was used to determine the change in enthalpy for a highly exothermic reaction, the combustion of magnesium metal. Enthalpy changes for the reactions of Mg in HCl (aq) and MgO (s) in HCl (aq) were determined experimentally, then added to that for the combustion of hydrogen gas to arrive at a value of –587 kJ/mol Mg.
...eases, including temperature. It is determined from the data that the reaction is more likely to have a step wise mechanism than a concerted due to the small – ΔS and a relatively large value of ΔH from the tables. Due to some errors, it is best to perform another experiment for future protocols. In addition with the variance the 35°C where at one point the absorbance levels off and then increases. In comparison to the rate constant against temperatures, at 25°C it is higher than 35 and 45. More test is required to ensure proper determination of the rate constant at those temperatures.
type of energy is lost or gained, and whether or not a factor that is
During this reaction the solution gained heat. This is what we were monitoring. The reason why the solution gained heat is because the reaction lost heat. Energy is lost when two elements or compounds mix. The energy lost/ gain was heat. Heat is a form of energy as stated above in the previous paragraph. The sign of enthalpy for three out of the four reactions matches what was observed in the lab. For the last reaction, part four, the reaction gained heat not the solution like parts one through three. The negative enthalpy value for part four indicates that the reaction gained
A precipitation reaction can occur when two ionic compounds react and produce an insoluble solid. A precipitate is the result of this reaction. This experiment demonstrates how different compounds, react with each other; specifically relating to the solubility of the compounds involved. The independent variable, will be the changing of the various chemical solutions that were mixed in order to produce different results. Conversely the dependent variable will be the result of the independent variable, these include the precipitates formed, and the changes that can be observed after the experiment has been conducted. The controlled variable will be the measurement of ten droplets per test tube.
In order for KNO3 to be dissolved, it must come into contact with
+70.48 kJ.mol. Comparing the value +70.48 kJ.mol-1 to the theoretical value of this enthalpy change (101kPa, 298K): +177.8 kJ.mol-1, there is a huge difference. Percentage error is calculated by: 100 x Theoretical Value - Actual Value. Theoretical Value Percentage error = (177.8 - 70.48) / 177.8 = 60.4%. Considering the scatter diagrams, they show the expected positive correlation.
The purpose of the experiment is to identify and understand reactions under kinetic and thermodynamic control. A reaction under kinetic and thermodynamic control can form two different types of products. A reaction under kinetic control is known to be irreversible and the product is formed quickly. A reaction under thermodynamic control is known to require rigorous conditions. It is also reversible. The final product is more stable than the product made by kinetic control. The chart below shows the two types of reaction coordinates:
n is the number of moles, R is the gas constant (8.31 J/Kmol), and ΔT is the change in temperature measured in Kelvins.
The gradient of the graph tells us whether the different rate curves have the same relation, meaning if they have a similar rate of reaction. Reactions can take place in a variety of customs; they can bee steep or steady. The steeper the slope, the faster the reaction takes place. The steadier the slope, the slower the reaction takes place. Aim:
Explain what is meant by an equilibrium constant. Was the value constant for all of your experiments? Should it be constant? The equilibrium constant demonstrates the relationship between the reactant and the products in the reaction. It shows the ratio of the products to the reactant when the reaction is at equilibrium and is represented by K. The equilibrium constant should remain constant because the only thing that effects the ratio of the products to reactants is temperature. It remains constant because of the Le Chatelier’s Principle which basically states when equilibrium is disturbed by changing conditions (pressure, adding a catalyst, adding more reactants, etc) the position of the equilibrium moves to counteract the change. The
Chemical kinetics is the study and examination of chemical reactions regarding re-arrangement of atoms, reaction rates, effect of various variables, and more. Chemical reaction rates, are the rates of change in amounts or concentrations of either products or reactants. Concentration of solutions, surface area, catalysts, temperature and the nature of reactants are all factors that can influence a rate of reaction. Increasing the concentration of a solution allows the rate of reaction to increase because highly concentrated solutions have more molecules and as a result the molecules collide faster. Surface area also affects a
Thermodynamics is the branch of science concerned with the nature of heat and its conversion to any form of energy. In thermodynamics, both the thermodynamic system and its environment are considered. A thermodynamic system, in general, is defined by its volume, pressure, temperature, and chemical make-up. In general, the environment will contain heat sources with unlimited heat capacity allowing it to give and receive heat without changing its temperature. Whenever the conditions change, the thermodynamic system will respond by changing its state; the temperature, volume, pressure, or chemical make-up will adjust accordingly in order to reach its original state of equilibrium. There are three laws of thermodynamics in which the changing system can follow in order to return to equilibrium.