Neutralization, enthalpy change acids

The standard enthalpy change for the ionization of water is +55.83 kJ mol", which means that the reverse reaction, which occurs when acids are neutralized by bases, is exothermic, i.e. ArH = —55.83 kJ mol-1. The corresponding change in standard Gibbs energy is —79.9 kJ mol - . The reaction ... 

Br0nsted-Lowry acid enthalpy change neutralization stepwise formation constant... 

The standard free energy for this reaction, AG°, is a measure of the gas-phase acidity of BH (AG°cid) or the gas-phase basicity of B (AG +). The standard enthalpy change for this reaction, AH°, is known as the proton affinity (PA) of the base B (a neutral or anionic species, depending on whether v = 1 or v = 0, respectively). The significance of these values lies in the fact that they are intrinsic in nature, as they are free of solvation contributions6 from both neutral and charged species in a bulk condensed phase. 

If 5.00 mol of NaOH dissolved in 250 mol of water is neutralized completely at 25°C with dilute phosphoric acid, what is the attendant enthalpy change ... 

A simpler device than the constant-volume calorimeter is the constant-pressnre calorimeter used to determine the heat changes for noncombnstion reactions. An operable constant-pressnre calorimeter can be constrncted from two Styrofoam coffee cnps, as shown in Fignre 6.7. This device measnres the heat effects of a variety of reactions, such as acid-base neutralization, as well as the heat of solntion and heat of di-Intion. Because the pressure is constant, the heat change for the process ( rxn) is equal to the enthalpy change (H). The measurements are similar to those of a constant-volume calorimeter—we need to know the heat capacity of the calorimeter, as well as the temperature change of the solution. Table 6.2 lists some reactions that have been studied with the constant-pressure calorimeter. 

In the case of a strong acid and a strong base, not only the salt, but also the reactants are completely dissociated. The reaction is effectively that between hydroxonium and hydroxyl ions, and it will apply for any strong acid with any strong base. As a result, we find that the enthalpy change of neutralization is approximately constant for any such reaction, and equals -56.07 kJ/mol. 

II) The enthalpy change of neutralization (AH ) is the standard enthalpy change when one mol of water is made in the neutralization of an acid by a base. Values are ... 

Figure 2. Enthalpy change (kilocalories/mole H ) on proton dissociation of alginic acid S-35, partially neutralized with KOH (O) and NaOH (9) in water at 25°C polymer concentration, 10 equiv/L.

An example of the enthalpy change of neutralization is from the reaction between sodium hydroxide solution and hydrochloric acid. The reaction can be described by the following thermochemical equation ... 

Figure 5.12 A graph of temperature versus volume of acid for an investigation to determine the enthalpy change of neutralization for an acid... 

A simple method for determining the enthalpy change of neutralization involves mixing equal volumes of dilute solutions of a strong acid and a strong base of known concentration and measuring the temperature rise. A thick plastic cup fitted with a lid makes a cheap and effective calorimeter. 

BO.OOcm of I.Omoldm-3 hydrochloric acid was added to BO.OOcm of I.Omoldm- sodium hydroxide solution. The temperature rose by 6.8°C. Calculate the enthalpy change of neutralization for this reaction. Assume that the density of the solution is I.OOgcm" and the specific heat capacity of the solution is4.18Jg °C . ... 

When strong bases neutralize strong acids in solutions that have molar concentrations of 1 mol dm-3, the enthalpy of the reaction is observed to be -55.83 kJ mol - irrespective of the counter ions (e.g. the chloride ion derivable from HC1 and the sodium ion contained in NaOH) present. For example, when a standard solution (1 mol dm-3) of hydrochloric acid is neutralized by a standard solution (1 mol dm-3) of sodium hydroxide, the change in enthalpy of the reaction is -55.83 kJ mol-1. Because the strong acid HCI and the strong base NaOH are 100% dissociated in aqueous solution, theucutruli/atiun reaction may be written as ... 

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