| 单词 | enthalpy |
| 例句 | And I didn’t know that the enthalpy decrease in a converging passage could be transformed into jet kinetic energy if a divergent passage was added. October Sky 1999-04-01T00:00:00Z Predicting the shift an equilibrium will experience in response to a change in temperature is most conveniently accomplished by considering the enthalpy change of the reaction. Chemistry 2019-02-14T00:00:00Z A baby developing from egg is an endergonic process, enthalpy decreases and entropy decreases. Biology for AP Courses 2022-06-09T00:00:00Z The free energy that we mentioned before is a combination of two variables, enthalpy and . Here's your Boeing 777, now make me the next Prozac. 2012-08-17T18:15:00.497Z Figure 8: Rate constant of current absorbents or adsorbents is about linearly proportional to the reaction enthalpy. Opportunities and challenges for a sustainable energy future 2012-08-15T17:21:52.727Z For an exothermic process, the products are at lower enthalpy than are the reactants. Chemistry 2019-02-14T00:00:00Z To illustrate this concept, the equation relating free energy change to the enthalpy and entropy changes for the process is considered: Chemistry 2019-02-14T00:00:00Z Sand art being destroyed is exergonic, no change in enthalpy and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z In general, if we multiply or divide an equation by a number, then the enthalpy change should also be multiplied or divided by the same number. Chemistry 2019-02-14T00:00:00Z The energy cost, however, depends on the enthalpy of the sorbent-CO dissociation reaction. Opportunities and challenges for a sustainable energy future 2012-08-15T17:21:52.727Z Then, for the “reverse” reaction, the enthalpy change is also “reversed”: Chemistry 2019-02-14T00:00:00Z What is the enthalpy of reaction per gram of quicklime that reacts? Chemistry 2019-02-14T00:00:00Z A ball rolling downhill is exergonic process, enthalpy decreases and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z We also can use Hess’s law to determine the enthalpy change of any reaction if the corresponding enthalpies of formation of the reactants and products are available. Chemistry 2019-02-14T00:00:00Z Figure 8: Rate constant of current absorbents or adsorbents is about linearly proportional to the reaction enthalpy. Opportunities and challenges for a sustainable energy future 2012-08-15T17:21:52.727Z The following example shows in detail why this equation is valid, and how to use it to calculate the enthalpy change for a reaction of interest. Chemistry 2019-02-14T00:00:00Z Both diagrams describe two-step, exothermic reactions, but with different changes in enthalpy, suggesting the diagrams depict two different overall reactions. Chemistry 2019-02-14T00:00:00Z Which of the terms in the Gibbs free energy equation denotes enthalpy? Biology for AP Courses 2022-06-09T00:00:00Z Summing their enthalpy changes gives the value we want to determine: Chemistry 2019-02-14T00:00:00Z Calculate the enthalpy of combustion of exactly 1 L of ethanol. Chemistry 2019-02-14T00:00:00Z Use this information to estimate the enthalpy of vaporization for isooctane. Chemistry 2019-02-14T00:00:00Z The given values for entropy and enthalpy are for NaCl at 298 K. It is assumed that these do not change significantly at the higher temperatures used in the problem. Chemistry 2019-02-14T00:00:00Z This total energy change in the system is called enthalpy and is denoted as ∆H . Biology for AP Courses 2022-06-09T00:00:00Z Use this information to estimate the enthalpy of vaporization for ethanol. Chemistry 2019-02-14T00:00:00Z The energy change associated with the vaporization process is the enthalpy of vaporization, ΔHvap. Chemistry 2019-02-14T00:00:00Z The enthalpy of sublimation, ΔHsub, is the energy required to convert one mole of a substance from the solid to the gaseous state. Chemistry 2019-02-14T00:00:00Z The heat given off when you operate a Bunsen burner is equal to the enthalpy change of the methane combustion reaction that takes place, since it occurs at the essentially constant pressure of the atmosphere. Chemistry 2019-02-14T00:00:00Z Compost pile decomposition is endergonic, enthalpy increases and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z Likewise, the enthalpy change for the reverse process of deposition is equal in magnitude but opposite in sign to that for sublimation: Chemistry 2019-02-14T00:00:00Z As a result, the enthalpy of fusion for a substance is less than its enthalpy of vaporization. Chemistry 2019-02-14T00:00:00Z Viewed in this manner, the enthalpy of sublimation for a substance may be estimated as the sum of its enthalpies of fusion and vaporization, as illustrated in Figure 10.28. Chemistry 2019-02-14T00:00:00Z In a thermochemical equation, the enthalpy change of a reaction is shown as a ΔH value following the equation for the reaction. Chemistry 2019-02-14T00:00:00Z A baby developing from egg is an endergonic process, enthalpy decreases and entropy decreases. Biology for AP Courses 2022-06-09T00:00:00Z The enthalpy of vaporization of water is larger than its enthalpy of fusion. Chemistry 2019-02-14T00:00:00Z Using the appendix data to calculate the standard enthalpy and entropy changes yields: Chemistry 2019-02-14T00:00:00Z Determine the standard enthalpy change, entropy change, and free energy change for the conversion of diamond to graphite. Chemistry 2019-02-14T00:00:00Z The enthalpy change of a reaction depends on the physical states of the reactants and products, so these must be shown. Chemistry 2019-02-14T00:00:00Z Sand art being destroyed is exergonic, no change in enthalpy and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z Discuss the spontaneity of the conversion with respect to the enthalpy and entropy changes. Chemistry 2019-02-14T00:00:00Z Let us determine the approximate amount of heat produced by burning 1.00 L of gasoline, assuming the enthalpy of combustion of gasoline is the same as that of isooctane, a common component of gasoline. Chemistry 2019-02-14T00:00:00Z Because D values are typically averages for one type of bond in many different molecules, this calculation provides a rough estimate, not an exact value, for the enthalpy of reaction. Chemistry 2019-02-14T00:00:00Z Since the provided amount of KClO3 is less than the stoichiometric amount, it is the limiting reactant and may be used to compute the enthalpy change: Chemistry 2019-02-14T00:00:00Z A baby developing from egg is an endergonic process, enthalpy decreases and entropy decreases. Biology for AP Courses 2022-06-09T00:00:00Z The approach used to calculate for a reaction from values is the same as that demonstrated previously for enthalpy and entropy changes. Chemistry 2019-02-14T00:00:00Z The spontaneity of a process, as reflected in the arithmetic sign of its free energy change, is then determined by the signs of the enthalpy and entropy changes and, in some cases, the absolute temperature. Chemistry 2019-02-14T00:00:00Z A process whose enthalpy and entropy changes are of the same arithmetic sign will exhibit a temperature-dependent spontaneity as depicted by the two yellow lines in the plot. Chemistry 2019-02-14T00:00:00Z These values are especially useful for computing or predicting enthalpy changes for chemical reactions that are impractical or dangerous to carry out, or for processes for which it is difficult to make measurements. Chemistry 2019-02-14T00:00:00Z Sand art being destroyed is exergonic, no change in enthalpy and entropy decreases. Biology for AP Courses 2022-06-09T00:00:00Z The bond energy for a diatomic molecule, DX–Y, is defined as the standard enthalpy change for the endothermic reaction: Chemistry 2019-02-14T00:00:00Z The sum of all bond energies in such a molecule is equal to the standard enthalpy change for the endothermic reaction that breaks all the bonds in the molecule. Chemistry 2019-02-14T00:00:00Z The enthalpy of a reaction can be estimated based on the energy input required to break bonds and the energy released when new bonds are formed. Chemistry 2019-02-14T00:00:00Z If we have values for the appropriate standard enthalpies of formation, we can determine the enthalpy change for any reaction, which we will practice in the next section on Hess’s law. Chemistry 2019-02-14T00:00:00Z A ball rolling downhill is exergonic process, enthalpy decreases and no change in entropy. Biology for AP Courses 2022-06-09T00:00:00Z Using the standard enthalpy of formation data in Appendix G, calculate the bond energy of the carbon- sulfur double bond in CS2. Chemistry 2019-02-14T00:00:00Z Enthalpy values for specific substances cannot be measured directly; only enthalpy changes for chemical or physical processes can be determined. Chemistry 2019-02-14T00:00:00Z Chemists usually perform experiments under normal atmospheric conditions, at constant external pressure with q = ΔH, which makes enthalpy the most convenient choice for determining heat changes for chemical reactions. Chemistry 2019-02-14T00:00:00Z This is the enthalpy change for the exothermic reaction: Chemistry 2019-02-14T00:00:00Z In each case, does enthalpy increase or decrease, and does entropy increase or decrease? Biology for AP Courses 2022-06-09T00:00:00Z Determine the enthalpy change per mole of zinc reacting for the reaction: Chemistry 2019-02-14T00:00:00Z We will include a superscripted “o” in the enthalpy change symbol to designate standard state. Chemistry 2019-02-14T00:00:00Z Thus, the symbol is used to indicate an enthalpy change for a process occurring under these conditions. Chemistry 2019-02-14T00:00:00Z This is the enthalpy change for the reaction: Chemistry 2019-02-14T00:00:00Z A ball rolling downhill is exergonic process, enthalpy decreases and no change in entropy. Biology for AP Courses 2022-06-09T00:00:00Z The enthalpy changes for many types of chemical and physical processes are available in the reference literature, including those for combustion reactions, phase transitions, and formation reactions. Chemistry 2019-02-14T00:00:00Z As we discuss these quantities, it is important to pay attention to the extensive nature of enthalpy and enthalpy changes. Chemistry 2019-02-14T00:00:00Z What is the enthalpy of combustion per mole of methane under these conditions? Chemistry 2019-02-14T00:00:00Z Assuming that both the reactants and products of the reaction are in their standard states, determine the standard enthalpy of formation, of ozone from the following information: Chemistry 2019-02-14T00:00:00Z Compost pile decomposition is exergonic, enthalpy increases and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z Assume both the reactants and products are under standard state conditions, and that the heat released is directly proportional to the enthalpy of combustion of graphite. Chemistry 2019-02-14T00:00:00Z We can use bond energies to calculate approximate enthalpy changes for reactions where enthalpies of formation are not available. Chemistry 2019-02-14T00:00:00Z For the ionic solid MX, the lattice energy is the enthalpy change of the process: Chemistry 2019-02-14T00:00:00Z Hess’s law is valid because enthalpy is a state function: Enthalpy changes depend only on where a chemical process starts and ends, but not on the path it takes from start to finish. Chemistry 2019-02-14T00:00:00Z Compost pile decomposition is exergonic, enthalpy increases and entropy increases. Biology for AP Courses 2022-06-09T00:00:00Z The enthalpy change in this step is the negative of the lattice energy, so it is also an exothermic quantity. Chemistry 2019-02-14T00:00:00Z The total energy involved in this conversion is equal to the experimentally determined enthalpy of formation, of the compound from its elements. Chemistry 2019-02-14T00:00:00Z Hess’s law can also be used to show the relationship between the enthalpies of the individual steps and the enthalpy of formation. Chemistry 2019-02-14T00:00:00Z According to Hess’s law, the enthalpy change of the reaction will equal the sum of the enthalpy changes of the steps. Chemistry 2019-02-14T00:00:00Z The enthalpy of fusion and the melting point of a crystalline solid depend on the strength of the attractive forces between the units present in the crystal. Chemistry 2019-02-14T00:00:00Z The amount of heat required to change one mole of a substance from the solid state to the liquid state is the enthalpy of fusion, ΔHfus of the substance. Chemistry 2019-02-14T00:00:00Z |
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