Energy changes

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Sorted FAQs on Energy Changes

This topic has attracted a lot of questions to Re:act over the years. To help you find the ones of most interest to you more easily, whether they are about background theory or a particular experiment, we have sorted the FAQs under several headings below, with a direct link to each question and answer.

1. Definitions and standard states
•Diamond or graphite as standard state?
•Standard states for atomisation?
•Difference between energy and enthalpy?
•What does STP stand for?
•Difference between enthalpy and entropy?
•Difference between heat and temperature?
•Sulphur allotropes: standard form for enthalpy and entropy?
2. Hess's Law
•Hess cycle for decomposition of KHCO₃ or KHCO₃ decomposition
•How to find enthalpy change for Cu + HCl using Hess cycle
•Alternative routes for Hess cycle?
•Bonding in benzene: use of Hess's law?
3. Calorimetry
•Sign of q in energy changes?
•Working out amount of heat - T in Kelvin?
•Source of energy when NaOH dissolves?
•Calorimetry: effect of concentration and volume on temperature changes?
•Does 'm' in q=mCT include mass of solute?
•How to find enthalpy changes for Zn + Cu²⁺ and Zn + H⁺
•Effect of volume on temperature change?
•Constructing a Hess cycle from separate equations
•Calorimetry and the Law of Conservation of Energy
•Number of readings?
•Approximations for calculations in calorimetry
•[Mg + Cu²⁺: method and calculations
4. Enthalpies of combustion
•Values for enthalpy of combustion for C_{1 - 4} alcohols
•How does structure affect heats of combustion for alcohols?
•How does structure affect heats of combustion for alcohols?
•How to calculate enthalpies of combustion of alcohols from lab measurements and Calculating heats of combustion
•Enthalpies of combustion for alcohols: difference between experimental and data book values or Low enthalpies of combustion values
•Effect of position of OH on enthalpies of combustion of alcohols? or Difference in heats of combustion for propanols and Why is enthalpy of combustion of propan-1-ol lower than propan-2-ol?
•Volume of fuel for given amount of energy?
•Questions about combustion of heptane
•Finding enthalpies of combustion of alcohols
5. Lattice energies
•Lattice enthalpies: why is value for MgO >> NaCl?
•Lattice and hydration enthalpy for NH₄Cl
6. Enthalpy of neutralisation
•Heat of neutralisation: acid or alkali in first? Concentrations?
•Heat of neutralisation: effect of volumes on accuracy?
•Why is heat of neutralisation same for many acids and alkalis?
•How to work out heat of neutralisation
•Concentration of NaOH using calorimetry
•Neutralisation enthalpy of strong & weak acids
7. Miscellaneous
•Enthalpy and entropy data for iron(II) and copper(II)carbonates?
•Why is NH₄NO₃ an explosive?
•Melting exo- or endo-thermic?
•Enthalpy changes from enthalpies of formation and combustion
•How hot is Bunsen flame?
•How to work out enthalpy change of formation?
•Calorimetry - intermolecular forces
•Use thermite reactions?
•Gas -> liquid: exo- or endothermic?
•Bond energy for O-F

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updated: 08 August 2008