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Chapter 6: Problem 41

What is meant by the standard enthalpy of a reaction?

Short Answer

Expert verified
The standard enthalpy of a reaction is the heat change that occurs during a specific chemical reaction, measured under standard conditions (1 atmosphere pressure and 25 degrees Celsius temperature), considering one mole of reactants and products in the reaction.

Step by step solution

01

Understanding What Enthalpy is

Enthalpy is a measure of total energy in a thermodynamic system. It includes the internal energy, which is the energy required to create the system, and the amount of energy required to make room for the system by displacing its environment and establishing its volume and pressure.
02

Comprehending 'Reaction Enthalpy'

The reaction enthalpy, also known as heat of reaction, refers to the enthalpy change during a chemical reaction. For an exothermic reaction, the enthalpy change is negative as heat is released. For an endothermic reaction, the enthalpy change is positive as heat is absorbed.
03

Understanding 'Standard Enthalpy of Reaction'

'Standard Enthalpy of Reaction' or 'Heat of Reaction at standard state' is the heat change that occurs during a chemical reaction, specifically measured under standard conditions i.e., at 1 atmosphere pressure and 25 degrees Celsius temperature. The amount of reactants and products are considered as one mole in the reaction. It is symbolized as \( ΔH° \).

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Most popular questions from this chapter

At \(25^{\circ} \mathrm{C},\) the standard enthalpy of formation of \(\mathrm{HF}(a q)\) is given by \(-320.1 \mathrm{~kJ} / \mathrm{mol} ;\) of \(\mathrm{OH}^{-}(a q),\) it is \(-229.6 \mathrm{~kJ} / \mathrm{mol} ;\) of \(\mathrm{F}^{-}(a q),\) it is \(-329.1 \mathrm{~kJ} / \mathrm{mol} ;\) and of \(\mathrm{H}_{2} \mathrm{O}(l),\) it is \(-285.8 \mathrm{~kJ} / \mathrm{mol} .\) (a) Calculate the standard enthalpy of neutralization of \(\mathrm{HF}(a q)\) $$ \mathrm{HF}(a q)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{F}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}(l) $$ (b) Using the value of \(-56.2 \mathrm{~kJ}\) as the standard enthalpy change for the reaction $$\mathrm{H}^{+}(a q)+\mathrm{OH}^{-}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l) $$calculate the standard enthalpy change for the reaction$$\mathrm{HF}(a q) \longrightarrow \mathrm{H}^{+}(a q)+\mathrm{F}^{-}(a q) $$

Which is the more negative quantity at \(25^{\circ} \mathrm{C}: \Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{H}_{2} \mathrm{O}(l)\) or \(\Delta H_{\mathrm{f}}^{\circ}\) for \(\mathrm{H}_{2} \mathrm{O}(g) ?\)

Define calorimetry and describe two commonly used calorimeters. In a calorimetric measurement, why is it important that we know the heat capacity of the calorimeter? How is this value determined?

A driver's manual states that the stopping distance quadruples as the speed doubles; that is, if it takes \(30 \mathrm{ft}\) to stop a car moving at \(25 \mathrm{mph}\) then it would take \(120 \mathrm{ft}\) to stop a car moving at \(50 \mathrm{mph}\). Justify this statement by using mechanics and the first law of thermodynamics. [Assume that when a car is stopped, its kinetic energy \(\left(\frac{1}{2} m u^{2}\right)\) is totally converted to heat.]

Define these terms: thermochemistry, exothermic process, endothermic process.
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