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Phosphorus pentabromide is a reactive, yellow solid of formula P Br 5, which has the structure [PBr 4] + Br − (tetrabromophosphonium bromide) in the solid state but in the vapor phase is completely dissociated to PBr 3 and Br 2.
PBr 3 evolves corrosive HBr, which is toxic, and reacts violently with water and alcohols. PBr 3 + 3 H 2 O → H 3 PO 3 + 3 HBr. In reactions that produce phosphorous acid as a by-product, when working up by distillation be aware that this can decompose above about 160 °C to give phosphine which can cause explosions in contact with air. [9]
The solid-state reaction route is the most widely used method for the preparation of polycrystalline solids from a mixture of solid starting materials. Solids do not react together at room temperature over normal time scales and it is necessary to heat them to much higher temperatures, often to 1000 to 1500 °C, in order for the reaction to occur at an appreciable rate.
For example, an increase in pressure due to decreasing volume causes the reaction to shift to the side with fewer moles of gas. [16] The reaction yield stabilizes at equilibrium but can be increased by removing the product from the reaction mixture or changed by increasing the temperature or pressure.
A simplified phase diagram for water, showing whether solid ice, liquid water, or gaseous water vapor is the most stable at different combinations of temperature and pressure In physics , a state of matter is one of the distinct forms in which matter can exist.
A typical phase diagram.The solid green line applies to most substances; the dashed green line gives the anomalous behavior of water. In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. [1]
The reaction of quadricyclane with DEAD is a 2σ + 2σ + 2π cycloaddition that on water takes place within 10 minutes at room temperature with 82% yield. The same reaction in toluene takes 24 hours at 80 °C with 70% yield. An emulsion reaction in fluorinated cyclohexane takes 36 hours and the neat reaction takes even longer (48 hours).
A solubility equilibrium exists when a chemical compound in the solid state is in chemical equilibrium with a solution containing the compound. This type of equilibrium is an example of dynamic equilibrium in that some individual molecules migrate between the solid and solution phases such that the rates of dissolution and precipitation are equal to one another.