Hot and Cold Lab Report Example | Topics and Well Written Essays - 1250 words

Hot and Cold - Lab Report Example Introduction It is a common phenomenon that whenever there is a chemical reaction in a system at constant pressure while, at the same time, there is no energy gained or lost to the surrounding; it is always evident that the system would either decrease or increase. In the first instance, energy will be lost in the form of heat if the reaction is exothermic when the system gets into thermal contact with the surrounding. On the other hand, energy will be gained in the form of heat if the reaction is endothermic when the system’s temperature decreases. Enthalpy, denoted by H, is the change in heat energy of a system at a constant pressure. The SI unit of energy, which is joule (J), is similar to that of enthalpy (Hughes). Enthalpy is known to be a safe function, and can be denoted as shown below; Heat absorbed = increase in enthalpy = H = Hfinal - Hinitial -----------(i) Adiabatic conditions arise when a system is configured in such a manner that there is no heat gained or lost b y the system. Therefore, in adiabatic processes the heat absorbed is always equal to enthalpy change, which is zero. Enthalpy can be changed by changing the temperature of water or even by a chemical reaction under adiabatic conditions as shown below; Hsystem = + Hdue to reaction = 0 ----------------(ii) Hdue to reaction = - -------------------(iii) Thus, enthalpy change can be calculated as follows; = Specific heat capacity x mass x T -----------(iv) Where; T = Tf - Ti For exothermic reactions, T is always positive and negative for endothermic reactions. If the measurement of change in temperature of any chemical reaction is taken under adiabatic condition then change in enthalpy due to the reaction, can be ascertained from the enthalpy change producing the change in temperature (Hughes). Enthalpy is an extensive property that in many occasions depends on the amount of reaction that occurs. Therefore, in order to obtain an intensive property in the comparison of various reactions, the enthalpy change is always related to the amount of one of the products or reactants. From this explanation, the enthalpy reaction may be given as shown below; H = ----------(v) The SI unit for Hrxn is given as J/mol, even though reaction enthalpies are normally said to be in kJ/mol. Species A may be taken as the limiting reagent since some of it needs to be reacted. In addition, reaction enthalpies are known to be calculated from values that are tabularized at standard molar enthalpies of formation, from tabulated combustion enthalpies, and from calorimetry data (Hughes). The experimental calorimetry data is the method that is chosen for this lab experiment using the various principles discussed above. The Calorimeter A calorimeter is a device that can be used in measuring the enthalpy change in a system during a reaction, but at the same time taking caution of the increase in temperature (for exothermic reaction), or decrease in temperature (for endothermic reaction) (Hughes). There are several types of calorimeter, but for this experiment the calorimeter used is the Styrofoam cups and plastic lids. Moreover, the foam between the surrounding and the liquid helps as the thermal obstacle in preventing heat loss from the reaction to the surroundings. The reactions will take place in a cup of aqueous solution, and the temperature monitored with the thermometer. There are two assumptions that ought to be made about the system and the calorimeter. First, the Styrofoam cup