Enthalpy of Neutralization
Enthalpy of Neutralization
Introduction
Energy changes always accompany chemical reactions. If energy, in the form of heat, is liberated the reaction is exothermic and if energy is absorbed the reaction is endothermic.
Thermochemistry is concerned with the measurement of the amount of heat evolved or absorbed. The heat (or enthalpy) of neutralization (∆H) is the heat evolved when an acid and a base react to form a salt plus water.
Eq. 1 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.
Heat measurements are performed by carrying out the reaction in a special container called a calorimeter. The heat (Q) given off by the neutralization reaction is absorbed by the reaction solution and the calorimeter. Both the solution and calorimeter increase in temperature due to the absorbed heat and this increase can be measured with a thermometer. ∆H is negative if heat is evolved and positive if heat is absorbed.
Eq. 2 -∆Hneutralization = QSolution + QCalorimeter
To evaluate the calorimeter constant (also known as its heat capacity) in J/oC, one adds a known mass of hot water to a known mass of cold water which is in the calorimeter. Heat
(Q) is lost by the hot water and is absorbed by the cold water and the calorimeter. Thus the heat absorbed by the calorimeter is the heat lost by the hot water minus the heat gained by the cold water.
QHot water = QCold water + QCalorimeter
Eq. 3 Qcalorimeter = QHot water - QCold water
It should be noted that we assume that the temperature of the calorimeter is the same as the solution inside it at all times. Q for both the hot and cold water is given by:
Eq. 4 Q = (4.184J/g-oC)(Mass in g)(∆t)
∆t is found by plotting temperature versus time for the system in the calorimeter and extrapolating the results to find ∆t at the instant of mixing (in this experiment, 5 minutes).
A typical
Introduction
Energy changes always accompany chemical reactions. If energy, in the form of heat, is liberated the reaction is exothermic and if energy is absorbed the reaction is endothermic.
Thermochemistry is concerned with the measurement of the amount of heat evolved or absorbed. The heat (or enthalpy) of neutralization (∆H) is the heat evolved when an acid and a base react to form a salt plus water.
Eq. 1 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.
Heat measurements are performed by carrying out the reaction in a special container called a calorimeter. The heat (Q) given off by the neutralization reaction is absorbed by the reaction solution and the calorimeter. Both the solution and calorimeter increase in temperature due to the absorbed heat and this increase can be measured with a thermometer. ∆H is negative if heat is evolved and positive if heat is absorbed.
Eq. 2 -∆Hneutralization = QSolution + QCalorimeter
To evaluate the calorimeter constant (also known as its heat capacity) in J/oC, one adds a known mass of hot water to a known mass of cold water which is in the calorimeter. Heat
(Q) is lost by the hot water and is absorbed by the cold water and the calorimeter. Thus the heat absorbed by the calorimeter is the heat lost by the hot water minus the heat gained by the cold water.
QHot water = QCold water + QCalorimeter
Eq. 3 Qcalorimeter = QHot water - QCold water
It should be noted that we assume that the temperature of the calorimeter is the same as the solution inside it at all times. Q for both the hot and cold water is given by:
Eq. 4 Q = (4.184J/g-oC)(Mass in g)(∆t)
∆t is found by plotting temperature versus time for the system in the calorimeter and extrapolating the results to find ∆t at the instant of mixing (in this experiment, 5 minutes).
A typical