Explain how the heat measured in Example 5.5 differs from the enthalpy change for the exothermic reaction described by the following equation:
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Chemistry 2e · 5.3 Enthalpy
Enthalpy: practice problems
23 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.
Exercises 41
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Key terms · 12
- chemical thermodynamics
- area of science that deals with the relationships between heat, work, and all forms of energy associated with chemical and physical processes
- enthalpy (H)
- sum of a system’s internal energy and the mathematical product of its pressure and volume
- enthalpy change (ΔH)
- heat released or absorbed by a system under constant pressure during a chemical or physical process
- expansion work (pressure-volume work)
- work done as a system expands or contracts against external pressure
- first law of thermodynamics
- internal energy of a system changes due to heat flow in or out of the system or work done on or by the system
- Hess’s law
- if a process can be represented as the sum of several steps, the enthalpy change of the process equals the sum of the enthalpy changes of the steps
- hydrocarbon
- compound composed only of hydrogen and carbon; the major component of fossil fuels
- internal energy (U)
- total of all possible kinds of energy present in a substance or substances
- standard enthalpy of combustion $\text{(} \text{Δ} H_{\text{c}}^{^\circ} \text{)}$
- heat released when one mole of a compound undergoes complete combustion under standard conditions
- standard enthalpy of formation $\text{(} \text{Δ} H_{\text{f}}^{^\circ} \text{)}$
- enthalpy change of a chemical reaction in which 1 mole of a pure substance is formed from its elements in their most stable states under standard state conditions
- standard state
- set of physical conditions as accepted as common reference conditions for reporting thermodynamic properties; 1 bar of pressure, and solutions at 1 molar concentrations, usually at a temperature of 298.15 K
- state function
- property depending only on the state of a system, and not the path taken to reach that state
Learn 5.3 on the whiteboard
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