Thermochemistry is the study of heat or energy from chemical reactions. Heat energy may be absorbed or released meaning the reaction is either endothermic or exothermic. Thermochemical reactions look at the heat in regards to the surroundings of the reaction to determine what type of reaction it is. The changes in heat are calculated by a calorimeter. Calorimeters calculate the change in heat by measuring the change in temperature and using the formula Q = mc ΔT, where Q is the heat of energy transferred, m is the mass of the calorimeter, c the specific heat of the calorimeter and ΔT being the change in temperature. This investigation looks at the combustion of alcohols and alkanes. Alkanes and alcohols are both hydrocarbons. Hydrocarbons are …show more content…
The results of each mixture were averaged out and the heat given out and the heat given off in KJ/g was measured by the heat formula Q = mc ΔT. The theoretical values were calculated using a mass fraction. The heat given off was measured using a calorimeter of water and how much heat it absorbed. The theoretical values were calculated by using a mass fraction. The prediction of this experiment was that the alkanes that had longer carbon chains would increase the amount of heat given off. However, the results did not follow this hypothesis. The average values of pentane and hexane had the highest amount of heat given off …show more content…
While hexane and octane had the lowest values of 15.4KJ/g for hexane and 10.44KJ/g for octane. This was in comparison to the average value of the control tests for pentanol which was 12.67KJ/g. Theses average values in comparison to the theoretical values of the tests are about half the value due to large percentage errors. These results reveal that the alkanes that have an odd number of carbon atoms in their chain released more heat than the alkanes with even numbers of carbon atoms in their chain. For example, pentane has 5 carbon atoms in its chain has a higher value than hexane which has 6 carbon atoms in its chain. The cause of this may be due to something called the Odd -Even Effect. This effect explains how even numbers of carbon atoms in the chain pack tighter together forming a crystal lattice, meaning that they have a higher melting point than odd numbered carbon chains. It also means that there is a difference between the temperature and vapor pressure relationship within even and odd numbered carbon chains. This odd even effect may somehow link to the combustion of alkanes and explain the results and why they did not follow the hypothesis. The results of this
It was desired to compare a theoretical value of enthalpy of combustion to a literature value. To do this, the theoretical value was calculated using a literature value for the heat of sublimation of naphthalene, the heat of vaporization of water and average bond energies, given in Table 1 of the lab packet.1 Equations (1) and (5) were used to calculate the theoretical enthalpy of combustion of gaseous naphthalene, where n was the number of moles, m was the number of bonds, and ΔH was the average bond energy:
For instance, pentan-1-ol, the alcohol utilised to synthesis 1-pentyl ethanoate, is relatively flammable due to the hydroxyl functional group attached to the molecule. Therefore, in order to prevent severe burns, a laboratory coat and safety glasses were worn. The experiment was additionally performed whilst standing up, so that if the aliquot of pentan-1-ol ignited,
In Experiment 10, the magnesium being burned included a large release of energy. The magnesium produced a bright light, showing that there was a chemical change and that the reaction was exothermic. The energy being released appears in the form of the light. Another example of an energy change is in Experiment 9. After the reaction between the copper II sulfate and the sodium carbonate, the test tube got colder, showing that this was an endothermic reaction, and that a chemical reaction had occurred.
Planning My aim for this experiment is to see the energy produced from different alcohols. This investigation involves burning alcohol in the air. ‘GCSE Chemistry’ by B.Earl and L.D.R Wilford says that "alcohols form, another homologous series, with the general formula Cn H2n+1OH ". The alcohol reacts with the oxygen in the air to form the products water and carbon dioxide.
Calorimetry is the analysis of energy changes in a certain system by determining how heat interacts within the system and with its surroundings. Bomb calorimetry, also known as constant volume calorimetry, is a method used in determining the enthalpy of combustion of a given hydrocarbon through the analysis of heat exchange in chemical reactions. The enthalpy of the substance is determined by many factors, including the heat capacity of the calorimeter, moles of substance lost during combustion, and the number of gas molecules lost post-combustion, to name a few. The relationship among the given factors were studied and applied in determining the enthalpy of combustion of a naphthalene (C10H8) sample. A standard bomb calorimeter, together with
Introduction: The theory behind this experiment is the heat of a reaction (∆E) plus the work (W) done by a reaction is equal to
According to the graph in figure 5, as the number of Carbon atoms in alcohol increased by 1, the change in standard enthalpy of combustion would increase by around 200 kJ/mol. This is proven as the equation of the linear line (protruding from the bottom left to the top right of the graph) is y=199.81x, where x is the number of Carbon atoms, y is the standard enthalpy of combustion and 199.81 is the gradient of the line and how much the standard enthalpy of combustion would increase by when multiplied by x. There were also errors/uncertainties that were shown in the graph and result tables. The average error of each of the different alcohols was of 6.51%. Thus, as the change in standard enthalpy of combustion of the alcohols increased, the uncertainties and errors became greater. The size of the uncertainties can be seen becoming greater as the size of the change in standard enthalpy of combustion increases in the graph of figure 5 and the results table of figure
Purpose: To measure the heats of reaction for three related exothermic reactions and to verify Hess’s Law of Heat Summation.
Introduction The importance of this lab is to see if the temperature changes during a chemical reaction. A chemical reaction is accompanied by a change in temperature. Endothermic reaction is when the temperature drops. Exothermic reaction is when the temperature rises.
The results that were revealed were thought to be accurate and reliable as many factors were controlled to enable the best quality. The results that a constant rise in the combustion occurred as each alcohol’s carbon chain increased with one exception indicates that the reliability of this experiment has to be examined. With such a high percentage error from these results means they cant be definitive. Also only three trials were conducted on the five different alcohols. If the experiment were to be conducted again I would conduct five trials on each alcohol to get a better average.
In order to measure the heats of reactions, add the reactants into the calorimeter and measure the difference between the initial and final temperature. The temperature difference helps us calculate the heat released or absorbed by the reaction. The equation for calorimetry is q=mc(ΔT). ΔT is the temperature change, m is the mass, c is the specific heat capacity of the solution, and q is the heat transfer. Given that the experiment is operated under constant pressure in the lab, the temperature change is due to the enthalpy of the reaction, therefore the heat of the reaction can be calculated.
Research Question: What impact does the number of carbon atoms in the homologous chain of alcohols have on the enthalpy change of combustion, when heating water to a temperature of 70 Celsius? SOI: “Chemistry has systems in place that are used when exploring chemical relationships.” Background Information: Alcohols are organic compounds that possess Oxygen, Carbon, Hydrogen and Carbon. The generic formula of alcohols is CnH2n+1OH, where n is a number.
Introduction: Every chemical change is accompanied by a change in energy usually in the form of heat. If heat is evolved, the reaction is exothermic, and if heat is absorbed, the reaction is endothermic. The energy change of a reaction that occurs at constant pressure is called the heat of reaction or the enthalpy of reaction (ΔHr). This quantity of heat is measured experimentally by allowing the reaction to occur in a calorimeter. In this experiment you will determine the heat of neutralization when an acid and a base react to form 1 mole of water. In a perfect calorimeter, heat is exchanged only between the reaction and the calorimeters water. Technically, some heat may may be absorbed the calorimeter. All calorimeters exchange some heat with its environment. This amount of heat is called the calorimeters heat capacity (the amount of of heat required to raise its temperature 1∘Celsius). We are going to “pretend” that our calorimeter is the perfect calorimeter.
In order to determine whether a hydrocarbon produced heat upon altering its chemical state, a bomb calorimeter was used to find the value of the heat of combustion for sucrose and an altoid mint. Using benzoic acid to calibrate the bomb calorimeter, the two samples were individually placed in a combustion cup within a stainless-steel cylinder enveloped in water, sealed shut by a shield containing a thermometer. After igniting the bomb, a change in temperature (°C) versus time (s) was recorded. Using the following equation, ∆T=T_c-T_A-r_1 (b-a)-r_2 (c-b), the ∆T of benzoic acid was 3.71°K. Which lead to the determination of the effective heat capacity, using C_(v,cal)=((∆cH_b-∆nRT/m_b ) m_b+C_Fe+C_N)/∆T, to be -9,666.27J/g
In this experiment, we investigate the change in temperature caused by adding a chemical substance into the water and dissolving it. The results recorded in the table below show that our hypothesis is correct.