Experiment 10: Thermochemistry: Hess\'s Law Determine the enthalpy of the ioniza

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Experiment 10: Thermochemistry: Hess's Law Determine the enthalpy of the ionization reaction of acetic acid Hess's Law will be used to calculabe the enthalpy change from two Back after the decimal point) is inserted through the hole Neutraization reaction is usualy accompanied excellent calorimeters because they can block the by release of heat as you have observed in experiment, you willmeasure the amount of heat The chemical reaction of interest ionization release when a chemical reaction takes place is ionization perfectly insulated, heat will not be able to flow through the walls of the calorimeter. Therefore, it have everything cancelled out: total heat transfer include any substance or substances that are substances that are dissolved in the water (the we add upall the sources of heat that are liberated and absorbed within the calorimeter, we should CHC00H(aq) CH3COO(aq) + H-(aq) (1) However, acetic acid is a weak acid and it will not take place in water on its own. Though one may consider the reverse reaction, CH,COO (aq) will form CH,COOH by taking H- from water as soon as CH COONa is added to water. This reaction cannot be run in water as written reactants and products of a chemical reaction) and The following reactions, however, can be run Since heat cannot flow through the wall of calorimeter, adding up all sources and sinks of heat will result in 0, or Qt O o 0-qreaction) + q(water)+ q(calorimeter) If the reaction is exothermic (iberates heat) their temperature will rise. Knowing the specific H'(aq) + OH-(aq) H2O or qreaction)- -q(water) -q(calorimeter) Taking a difference between (2) and (3), one can generate (1). Therefore, if you measure heat of reactions for (2) and (3), or AH2 and AHs, you will be able to calculate the heat of reaction of ionization of acetic acid, ,, accoring to Hess's Law of heat summation. heat of water (Cw, 4.184 J/goC), heat capacity of the calorimeter (Coc. 1.0x10 JC), and temperature absorbed can be calculated using the folowing q(water) C, x mass of H,Ox AT The heat evolved or absorbed during these change (AT T -T, the amount of heat that was reactions will be measured with a coffee-cup calorimeter (see procedure section). Y perform two trials of (2) and (3). Also, you will pool your data with your classmates to perform tistical analysis. Pooling the data will improve the precision of the measured enthalpy changes. q(calorimeter) Coe AT Keep in mind that this is only an approximation, because we are not dealing with pure water. When substances are dissolved in the water, their specific heat is altered somewhat. Coffee Cup Calorimeter Let's take a look at an example. In a coffee- The coffee cup calorimeter is constructed by nesting a Styrofoam cup inside of the second cup and covering it. A precision thermometer (you have to read this thermometer down to 2 digits cup calorimeter, 50 mL of 1.0 M base 50 mL of 1.0 M acid both at 253-c were mixed well as temperature increased to 31.8 °C

Explanation / Answer

1) For NaOH - HCl pair the neutralization reaction will be,

NaOH + HCl --------> NaCl + H2O

For NaOH - CH3COOH pair the neutralization reaction will be,

NaOH + CH3COOH --------> CH3COONa + H2O

Both the reactions are acid-base reactions where sodium salt and water is formed.

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