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Thermochemistry and questions
Thermochemistry essay
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Heats of Reaction and Hess’s Law Lab
Background: Thermochemistry is the branch of chemistry that deals with the amounts of heat evolved or absorbed during chemical reactions. When the pressure is constant, the amount of heat gained or lost in a chemical or physical change is the enthalpy change for the process, or heat of reaction. Heat of reaction can be calculated by using Hess’s Law which states that the heat released or absorbed in a chemical process is the same whether the process takes place in one or in several steps, also known the law of constant heat summation. By using Hess’s Law, the heat of reaction can be determined without actually measuring the enthalpy change. This is extremely helpful because some reactions are very difficult to find the heat of reactions for directly. This experiment will find the heat of reaction for two chemical reactions and require Hess’s Law to determine the heat of reaction for the final desired product.
Calorimetry is the science that determines the changes in energy of a system by measuring the heat exchanged with the surroundings. It often requires the use of a calorimeter which is an instrument for measuring the amount of heat involved in a chemical reaction. In this experiment, the first two reactions are exothermic so the temperature of the solution and container will rise and some heat will be lost to the surroundings.
Purpose: The purpose of this experiment is to calculate the heat of formation of magnesium oxide by studying a series of reactions involving magnesium and magnesium oxide and using Hess’s Law.
Hypothesis: If the heat of reaction is found for two equations, then Hess’s Law will be able to determine the heat of reaction of the desired product.
Materials:
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...actual heat of reaction for Part II was -146kJ/mole. The heat of formation found for the formation of liquid water was -286kJ/mole. By using Hess’s Law, the heat of reaction for the formation of magnesium oxide was found to be -496kJ/mole which yielded a -17.6% error.
A possible source of error could be loss of heat during the reaction that could have affected the final temperature results. Since a real calorimeter wasn’t used and a plastic cup calorimeter was used, there is a good chance that the system lost more heat to the surroundings than it would have if a real calorimeter had been used. That said, using the plastic cup calorimeter is a good substitute for a real calorimeter in classroom laboratory experiment because it still acts as an insulator to keep the heat inside and makes a better calorimeter than other materials because of its high specific heat.
Thermodynamics is essentially how heat energy transfers from one substance to another. In “Joe Science vs. the Water Heater,” the temperature of water in a water heater must be found without measuring the water directly from the water heater. This problem was translated to the lab by providing heated water, fish bowl thermometers, styrofoam cups, and all other instruments found in the lab. The thermometer only reaches 45 degrees celsius; therefore, thermodynamic equations need to be applied in order to find the original temperature of the hot water. We also had access to deionized water that was approximately room temperature.
== = 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.
The mass of Mg + the mass of O2=mass of MgxOx. Knowing the mass of
the acid was at 14 C the magnesium took 141 seconds to react and 27 C
Total energy difference is 1840 kJ/mol – 1371.5 kJ/mol = 469 kJ/mol, which indicates that the reaction is endothermic and that 469 kJ of heat is needed to be supplied to carry out this reaction.
If the pot is close to the heat source, more heat is directed to the water so it will be heated faster. Alcohols: Different alcohols have different bond structures, some bonds need more energy to break them than others, and some release more energy when they are broken. Temperature increase: I could change the amount the temperature has to rise before I record my results. This will only affect the amount of fuel used, so hasn’t got much relevance to the experiment. If I did a calculation from the results I have for the temperature rising to 10 c then I would be able to work out how much fuel would be used, if I heated the water to 50 c. X 10 x 50" By dividing the amount of fuel used by the temperature raised you will be given the amount of fuel used per c. If you multiply the amount of fuel used per c, by the amount you want to find results for, you will be given an exact amount for how much fuel would be used if you heated the water to that specific temperature.
The Effect of Temperature on The Rate Of Reaction Between Magnesium And Hydrochloric Acid Planning I'm planning on investigating how temperature effects the reaction between magnesium and hydrochloric acid, the experiment will show whether the reaction will speed up or slow down with the change in temperature. Temperatures will range from room temp up until 70 degrees. The investigation will be a fair test because all quantities will remain the same for each test, each test will use the same amounts of hydrochloric acid and same size of magnesium, also the concentration of the acid will also not be changed. APPERATUS; · Conical flask · Bunsen Burner · Thermometer · Tri-pod · Protective matt · Stopwatch · Gauze · Measuring jug · Goggles
" This means that therefore the enthalpy change of a reaction can be measured by the calculation of 2 other reactions which relate directly to the reactants used in the first reaction and provided the same reaction conditions are used, the results will not be affected. We have the problem set by the experiment to determine the enthalpy change of the thermal decomposition of calcium carbonate. This is difficult because we cannot accurately measure how much thermal energy is taken from the surroundings and provided via thermal energy from a Bunsen flame into the reactants, due to its endothermic nature. Therefore, using the enthalpy changes obtained in reaction 1 and reaction 2 we can set up a Hess cycle.
For the sample calculations, let’s use the marshmallow as an example. Its initial mass was 0.66 grams and its final mass was 0.36 grams. To calculate the amount burned, subtract 0.36 from 0.66 to get 0.30 grams. (Mass burned = mi- mf). To find the marshmallow’s change in temperature, use the formula (ΔT =
Mass of O = Mass of crucible, cover, KClO3 and MnO2 after heating (Step # 11) - Mass of crucible, cover, KClO3 and MnO2 before heating (Step # 5)
In this lab, I determined the amount of heat exchanged in four different chemical reactions only using two different compounds and water. The two compounds used were Magnesium Hydroxide and Citric Acid. Both compounds were in there solid states in powder form. Magnesium Hydroxide was mixed with water and the change in heat was measured using a thermometer. The next reaction combined citric acid and magnesium hydroxide in water. The change in heat was measured as well. For the third reaction citric acid was placed in water to measure the change in heat. In the last reaction, citric acid was combined with water. The heat exchanged was again measured. It is obvious we were studying the calorimetry of each reaction. We used a calorimeter
The Effect of Temperature of Hydrochloric Acid on the Rate of Reaction Between Hydrochloric Acid and Magnesium
Aim: The aim of this experiment was to determine the empirical formula of magnesium oxide.
The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction with Magnesium Aim: To investigate the effect of concentration of hydrochloric acid on the rate of reaction with magnesium Prediction: As the concentration of the hydrochloric acid increases, so will the rate of reaction Hypothesis: In a reaction, particles of two different reactants react together to form a product. The reaction only takes place on account of two things, if the particles collide, and if the collision has enough 'activation energy'. The two reactant particles, in this case magnesium particles and hydrochloric acid particles, must collide with each other on the correct 'collision course'. If this does not occur then no chemical reaction will take place. The reaction must also have enough energy, this can be affected by temperature, the more heat the particles have the faster they move and so the more energy therefore more chance of successful collisions.
Based on your experiments what is the formula of the colorless gas that is released when heating the malachite?