Search results
Results From The WOW.Com Content Network
In thermochemistry, a thermochemical equation is a balanced chemical equation that represents the energy changes from a system to its surroundings.One such equation involves the enthalpy change, which is denoted with In variable form, a thermochemical equation would appear similar to the following:
Enthalpy change of solution in water at 25 °C for some selected compounds [2] Compound ΔH o in kJ/mol; hydrochloric acid: −74.84 ammonium nitrate +25.69 ammonia: −30.50 potassium hydroxide: −57.61 caesium hydroxide: −71.55 sodium chloride +3.87 potassium chlorate +41.38 acetic acid: −1.51 sodium hydroxide: −44.50
It is a white crystalline salt that is highly soluble in water. Solutions of ammonium chloride are mildly acidic. In its naturally occurring mineralogic form, it is known as salammoniac. The mineral is commonly formed on burning coal dumps from condensation of coal-derived gases. It is also found around some types of volcanic vents.
An endothermic process may be a chemical process, such as dissolving ammonium nitrate (NH 4 NO 3) in water (H 2 O), or a physical process, such as the melting of ice cubes. [ 5 ] The opposite of an endothermic process is an exothermic process , one that releases or "gives out" energy, usually in the form of heat and sometimes as electrical ...
Endothermic reactions absorb heat, while exothermic reactions release heat. Thermochemistry coalesces the concepts of thermodynamics with the concept of energy in the form of chemical bonds. The subject commonly includes calculations of such quantities as heat capacity, heat of combustion, heat of formation, enthalpy, entropy, and free energy.
For elements that have multiple allotropes, the reference state usually is chosen to be the form in which the element is most stable under 1 bar of pressure. One exception is phosphorus, for which the most stable form at 1 bar is black phosphorus, but white phosphorus is chosen as the standard reference state for zero enthalpy of formation. [2]
A classical example is the decomposition of mercuric oxide to give oxygen and mercury metal. The reaction was used by Joseph Priestley to prepare samples of gaseous oxygen for the first time. When water is heated to well over 2,000 °C (2,270 K; 3,630 °F), a small percentage of it will decompose into OH, monatomic oxygen, monatomic hydrogen, O ...
The definition of the Gibbs function is = + where H is the enthalpy defined by: = +. Taking differentials of each definition to find dH and dG, then using the fundamental thermodynamic relation (always true for reversible or irreversible processes): = where S is the entropy, V is volume, (minus sign due to reversibility, in which dU = 0: work other than pressure-volume may be done and is equal ...