MD Asmik Kostyunina CHEMICAL REACTIONS - A branch of chemistry that studies the thermal effects of chemical reactions is called thermochemistry. All chemical processes are accompanied by the release or absorption of heat. Reactions accompanied by the release of heat from the system into the environment are called exothermic, accompanied by the absorption of heat from the environment, are called endothermic. The thermal effect of the reaction, measured at constant temperature and pressure, is called the heat of reaction Qр, and the opposite value in sign, which describes the change in the state of the system as a result of the reaction enthalpy deltaH.
Calorimeter - The experimental technique used to determine enthalpy is called calorimetry.
- The thermal effects of reactions are determined both experimentally and using thermochemical calculations. it is impossible to determine the absolute values of the internal energy of the enthalpy
How to experimentally determine the reaction enthalpy? - a typical calorimetric experiment consists due to the fact that the energy released as a result of a chemical transformation is transferred to water or a mixture, after which the increase in their temperature is measured by a thermometer
- HNO2(aq) + NAOH(aq) → NaNO2(aq) + H2O(l) + Q
- Q in the above equation is -∆H and is expressed in kJ/mol of water. Neutralization reactions are generally exothermic and thus ∆H is negative.
Determination of the thermal effect of the neutralization reaction. - According to the theory of electrolytic dissociation, the neutralization reaction will proceed according to the equation:
- NaOH + HCl = NaCl + H2O
- The task: Determine the heat of neutralization of a strong acid with a strong base and calculate the Gibbs energy of the reaction.
Calorimetric Setup Method of determination: - Measure with a cylinder 10 ml of a 1M acid solution and add to a calorimetric beaker. The calorimetric glass should be weighed with an accuracy of 00.00 g
- Measure the temperature of the solution with an accuracy of 0.010 C. before the reaction
- Measure with a cylinder 10 ml of 1M alkali solution.
- Provide reaction of neutralization into the calorimetric glass and measure the maximum temperature that the thermometer will show after draining the solutions.
- Collect Data: Temperature Difference (K)
- Mass of internal glass (kg)
- Mass of neutralized solution(l)
HCl + NaOH = NaCl + H2O + Q - Temperature difference:
- Mass of liquid in a calorimetric glass: p=1g/ml
- m2 = V * p (kg)
- System heat capacity: ƩC= (C1 * m1) + (C2 * m2)
Where: - C1= 0.75 · 10 J / kg · K is the specific heat of glass;
- C2= 4.18 · 10³ J / kg · K is the specific heat of the liquid.
ϪΤ = T(end)-T(start)
HCl + NaOH = NaCl + H2O + Q - The amount of heat released during the reaction:
- Q = ƩC * ϪΤ, J
- The number of moles of water, given that from 1 mol of alkali, 1 mol of water is obtained, C(Acid) = C(Alkali) = 1 mol / l:
- For example: n(H2O) = 25 ml * 1 mole / 1000,
- n(H2O)=0,025mole
- Practical change in the enthalpy of the neutralization reaction: ϪH = kJ/mole
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