The Determination of an Equilibrium Constant
Introduction:
PARTâ… : Theory
Many chemical reactions are irreversible reactions, for example, if
magnesium is burnt in air a brilliant white flame is observed as the
white powdery solid magnesium oxide is formed:
[IMAGE]2Mg(s) + O2(g) 2MgO(s)
We also say that the reaction goes to completion (as Fig. 1 shows),
and for practical purpose it is. Some apparently irreversible
reactions are reversible to such a small extent that we can ignore it.
[IMAGE]
[IMAGE] Concentration
[IMAGE]
Reaction stops when concentration reaches zero
[IMAGE]
[IMAGE] Time
Fig. 1
A reversible reaction is one that can take place in both directions
and so is incomplete (thus this symbol [IMAGE] is used). Take the
reaction between hydrogen and iodine for example:
H2(g) + I2(g) [IMAGE] 2HI(g)
0.5 moles of hydrogen gas and 0.5 moles of iodine gas react in sealed
glass bulbs and the temperature is kept constant at 445 °C. One may
assume that there would be 0.1 mole of hydrogen iodide present when
the reaction has completed but this is not the case. After 84 minutes,
there are only 0.78 moles of hydrogen iodide present. No matter how
much time elapsed after 84 minutes, the amounts of all three chemicals
were identical: the reaction has reached its equilibrium position
(Fig. 2).
[IMAGE][IMAGE] Equilibrium reached: no further changes
[IMAGE][IMAGE]Concentration
[IMAGE][IMAGE] Concentration of product
[IMAGE] Concentration of reactant
[IMAGE] Time
Fig. 2
However, it does not mean that the reaction has stopped. In fact both
the forward and the reverse reactions still continue, which is why we
use the term dynamic equilibrium:
When a reaction is in dynamic equilibrium, the forward and reverse
reactions are occurring at the same rate (Fig. 3).
[IMAGE][IMAGE] Forward rate Equilibrium reached
[IMAGE][IMAGE][IMAGE]Rate of
reaction
[IMAGE]
[IMAGE] Back rate
[IMAGE] Time
Fig. 3
Equilibrium is maintained only in a closed system, where there is no
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. Purpose
Next, we measured 1.07 g of magnesium oxide, using a balance in the fume hood, added it to the HCl in the calorimeter, and shut the lid quickly to conserve heat. This mixture was “swirled” and allowed a few moments to react. The final temperature was recorded and DT determined. GRAPH GRAPH
For these calculations assume the temperature remains constant at 25 °C. There are four steps here. First the initial concentration of CoCl2(iPrOH)2 needs to be determined. Second, the equilibrium concentration of CoCl2(iPrOH)2 must be found. Third is the calculation of the equilibrium concentration of CoCl2(MeOH)4, then fourth, the ratio [CoCl2(MeOH)4] / [CoCl2(iPrOH)2] at equilibrium. Show all work. Remember to state the equations you are using defining all variables and constants. Then substitute in the values and show the results. Be certain all sig figs and units are correct. You are expected to follow this format in all subsequent lab work without being prompted.
2) I accidently didn’t change my answer on my lab underneath the graph so I do apologize for that, but I feel that my hypothetical equilibrium state did almost reach my predicted number. The reason why I say this is because my predication number was only like I want to say roughly around 4 and it came bout between 2 & 3. I was kind of confused when I wrote 0.16, that is why it has a question mark and again I apologize for not changing it.
The objective of this lab is to find the equilibrium constant of Fe(SCN)2+ through multiple trials using a spectrometer. Since one chemical is colorless and the other is colored a spectrometer can be used to monitor amounts of each in the solution. By completing multiple trials an average can be reached for the value of the equilibrium constant of Fe(SCN)2+.
The experimental data suggest that calcium chloride (CaCl2) is the best salt to include in a hot pack because it was the most exothermic out of the tested salts. The average heat of reaction (q_(rxn,p)) of CaCl2 was calculated to be -460J. Additionally, the low cost of CaCl2 makes it an ideal choice for the widespread use of hot packs. Although the value for MgSO4 (average qrxn -443), the cost is over six times higher. Another issue to consider is the safety and toxicity of the product. According to the PubChem Open Chemistry Database calcium chloride can cause cough, sore throat and a burning sensation when inhaled (1). It can also cause redness, dry skin, and skin burns when it comes into contact with the skin. If ingested, CaCl2 can cause
by the amount of C02 produced by the reaction or by the amount of 02 consumed.
The Gravimetric Stoichiometry lab was a two-week lab in which we tested one of the fundamental laws of chemistry; the Law of Conservation of Mass. The law states that in chemical reactions, when you start with a set amount of reactant, the product should theoretically have the same mass. This can be hard sometimes because in certain reactions, gases are released and it’s hard to measure the mass of a gas. Some common gases released in chemical reactions include hydrogen, carbon dioxide, oxygen and water vapor.
== == = The formula for the chemical reaction is: = ==
As with all markets and their respective economies, having equilibrium is one of the key factors of a successful system. Although most markets do not reach equilibrium, they attempt at getting close. There are numerous methods devised to reach equilibrium, whether they involve human intervention directly or a cumulative decision by all factors involved. These factors may be a seller's willingness to lower overall revenue, or a buyer's willingness to withhold some demand for a certain product. Of course, the basics of supply and demand retrospectively control the equilibrium in the market.
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:
In the absence of government intervention, price is determined by demand and supply. The equilibrium price is where demand and supply are equal. At this point there are no forces causing the price to change. The quantity which consumers want to buy will equal the quantity which producers want to sell at the current price.
stress is built, and finally, the body enters a stage of exhaustion, a sort of aging "due to wear and tear" (Andrews, Cromwell, Fries & Hodge, 2008).
This explains why the rate of reaction is highest when the reactants are
The rate of reaction is how quickly or slowly reactants in chemical reactants turn into products. A low reaction rate is when the reaction takes a long time to take place; hence, a reaction that occurs quickly has a high reaction rate. A rate refers to how slow or quick the product is produced. It is possible to control the rate of chemical reactions and speed up or slow down the rate of chemical reactions by altering three main factors which are temperature, concentration and the surface area. When the temperature of the reactants increases, the molecules vibrate at a more intense speed therefore colliding with each other more frequently and with increased energy resulting in a greater rate of reaction. Accordingly, as the temperature decreases the molecules will move slower, colliding less frequently and with decreased energy resulting in the rate of reaction decreasing. Concentration is how much solute is dissolved into a solution and is also a factor that affects the rate of reaction. When the concentration is greater this means there is an increased amount of reactant atoms and molecules resulting in a higher chance that collisions between molecules will occur. A higher collision rate means a higher reaction rate. Consequently at lower concentrations there are reduced chances of the molecules colliding resulting in a lower reaction rate. The measurement of how much an area of a solid is exposed is called the surface area. The quicker a reaction will occur the more finely divided the solid is. For example, a powdered solid will usually have a greater rate of reaction in comparison to a solid lump that contains the same mass for it has a lower surface area than the powdered solid.