Question

almost all gases have the same RVP at

A) same temperture and pressure

B) same critical temperture and critical pressure

C) at standard temperture and pressure

Answer 1

Ans B

Reid vapor pressure (RVP) is a common measure of the volatility of gasoline and other petroleum products . It is defined as the absolute vapor pressure exerted by a liquid (and any dissolved gases/moisture) at 37.8 °C (100 °F) . The test method measures the vapor pressure of gasoline, volatile crude oil, jet fuels, naphtha, and other volatile petroleum products but is not applicable to liquefied petroleum gases . It requires that the sample be chilled to 0-1 degrees Celsius and then poured into the apparatus ; for any material that solidifies at this temperature, this step cannot be performed. RVP is commonly reported in kilopascals or pounds per square inch  and represents volatization at atmospheric pressure because measures the gauge pressure of the sample in a non-evacuated chamber.

The matter of vapor pressure is important relating to the function and operation of gasoline-powered, especially carbureted, vehicles and is also important for many other reasons. High levels of vaporization are desirable for winter starting and operation and lower levels are desirable in avoiding vapor lock during summer heat. Fuel cannot be pumped when there is vapor in the fuel line (summer) and winter starting will be more difficult when liquid gasoline in the combustion chambers has not vaporized. Thus, oil refineries manipulate the Reid Vapor Pressure seasonally specifically to maintain gasoline engine reliability.

The Reid vapor pressure (RVP) can differ substantially from the true vapor pressure (TVP) of a liquid mixture, since

(1) RVP is the vapor pressure measured at 37.8 °C (100 °F) and the TVP is a function of the temperature.

(2) RVP is defined as being measured at a vapor-to-liquid ratio of 4:1, whereas the TVP of mixtures can depend on the actual vapor-to-liquid ratio.

(3) RVP will include the pressure associated with the presence of dissolved water and air in the sample (which is excluded by some but not all definitions of TVP)

(4) the RVP method is applied to a sample which has had the opportunity to volatize somewhat prior to measurement: i.e., the sample container is required to be only 70-80% full of liquid (so that whatever volatizes into the container headspace is lost prior to analysis) the sample then again volatizes into the headspace of the test chamber before it is heated to 37.8 degrees Celsius.