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Heat of Neutralization. Objective: To investigate the enthalpy changes () of various acid-base neutralizations.

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Title: Heat of Neutralization Objective: To investigate the enthalpy changes () of various acid-base neutralizations. Chemicals and Apparatus: 1.0M hydrochloric acid, ~1.0M sodium hydroxide solution, one thermometer, one polystyrene foam cup with lid, two pieces of 50.00 burette, two filter funnels, one piece of 25.00 pipette, pipette filler and a 100 beaker. Background: All chemical reactions involve energy changes. The study of energy changes is an important part of chemistry. Fundamental to the thermo-chemistry is the law of conservation of energy, which states that energy is neither created nor destroyed, but can be converted from one form to another. An exothermic reaction is one in which stored chemical energy is converted to heat energy (heat is released to the surroundings), conversely an endothermic reaction is one in which heat energy is converted to chemical energy (heat is absorbed into the system). The enthalpy (H) of a substance, sometimes called its heat content, is an indication of its total energy content. The equation for calculating the enthalpy change (heat change) is given by ?H = -m x c x ?T where m is the mass of the sample, c is the specific heat capacity of the sample and ?T is the change in temperature. The sign for ?H indicates the direction of heat flow, positive for endothermic processes and negative for exothermic processes. In this experiment, we were going to determine the enthalpy changes for a specific pair of acid-base neutralization. ...read more.


of acid(aq) added 0.0 2.0 4.0 6.0 8.0 10.0 12.0 Max. Temp. 22.4 22.9 23.7 24.5 25.0 25.6 26.0 Vol. of acid(aq) added 14.0 16.0 18.0 20.0 22.0 24.0 26.0 Max. Temp. 26.4 26.8 27.0 27.3 27.6 27.8 28.0 Vol. of acid(aq) added 28.0 30.0 32.0 34.0 36.0 38.0 40.0 Max. Temp. 28.2 28.2 27.8 27.7 27.6 27.5 27.5 (A large scale graph would be attached at page 12) The maximum temperature during the experiment was The volume of acid (aq) added to the experiment while the maximum temperature reached was 25.5. No. of mole of acid No. of mole of alkaki Molarity of alkali ?H = -m x c x ?T = -(25.50+25.00) x 4.184 x (28.3-22.4) = -47.5 x 4.184 x 5.9 = -1246.623J The enthalpy change of neutralization Discussion: 1. Every chemical change is accompanied by a change in energy, usually in the form of heat. The energy change of a reaction that occurs at constant pressure (i.e. atmospheric pressure) is termed the heat of reaction or the enthalpy change. If heat is evolved, the reaction is exothermic and if heat is absorbed, the reaction is endothermic. 2. The first law of thermodynamics states that heat is not lost, gained, or destroyed. Only it is transformed from one form to another. The second law is shown by the material gaining the heat moving from the material losing heat. ...read more.


And the enthalpy of neutralization was the heat produced when an acid and a base react together in aqueous solution to produce one mole of water. Strong acids (e.g. hydrochloric acid, sulfuric acid or nitric acid) and strong alkalis were completely dissociated in dilute solution, so the reaction between any strong acid and strong alkali might be represented as following: If a weak acid or alkali were used, or if both were weak, then the enthalpy of neutralization was usually lower than. This was because weak acids and weak alkalis were only slightly ionized in aqueous solution, and energy was absorbed in ionizing the unionized molecules. The enthalpies of reactions and Hess's Law would be used to calculate the enthalpy change for the reaction which was not directly observed. Recall that since enthalpy was a state function, the enthalpy change for any process would depend only on the starting and ending points, not on the reaction path followed. The enthalpy, ?H, changes for the reaction, we used the acid-base combination of group 3 as an example: , can be written as Since ?H' is positive, the value had to smaller than the value of the combination of strong acid and alkali because, so the value of is less negative then that of. Hazards: The diluted hydrochloric acid and aqueous ammonia were corrosive to equipment and skin. They were also volatile, therefore, be very careful to keep their vapors out of the room. The dilute acid, base, and salt solutions might all be flushed directly down the sink with lots of water. ?? ?? ?? ?? - 1 - ...read more.

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This is a very good report. It has a detailed, reliable method and excellent graphs of results. The calculations within it are set out very well and allow valid conclusions to be drawn.

Marked by teacher Brady Smith 14/12/2012

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