The Smoking Hills are located on the east coast of Cape Bathurst in Canada 's Northwest Territories , next to the Arctic Ocean and a small group of lakes. The cliffs were named by explorer John Franklin , who was the first European to see them on his 1826 expeditions. They contain strata of hydrocarbons ( oil shales ), which have been burning continuously for centuries.
30-542: The fires result from autoignition of sulfur-rich lignite deposits. The clouds of smoke have given the region its name. Over time the sulfur dioxide from the smoke has acidified the shallow ponds (< 1 hectare (2.5 acres) area and < 1 m (3 ft 3.4 in) depth) in the tundra dotting the area, down to a pH lower than 2. Elevated concentrations of metals (aluminium, iron, zinc, nickel, manganese and cadmium) occur in these acidic ponds. Soils and sediments have also been chemically altered. The acidic biota in
60-423: A substance is the lowest temperature at which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark . This temperature is required to supply the activation energy needed for combustion . The temperature at which a chemical ignites decreases as the pressure is increased. Autoignition temperatures of liquid chemicals are typically measured using
90-483: A 500-millilitre (18 imp fl oz; 17 US fl oz) flask placed in a temperature-controlled oven in accordance with the procedure described in ASTM E659. When measured for plastics , autoignition temperature can also be measured under elevated pressure and at 100% oxygen concentration. The resulting value is used as a predictor of viability for high-oxygen service. The main testing standard for this
120-460: A function of partial pressure. Using diving terms, partial pressure is calculated as: For the component gas "i": For example, at 50 metres (164 ft) underwater, the total absolute pressure is 6 bar (600 kPa) (i.e., 1 bar of atmospheric pressure + 5 bar of water pressure) and the partial pressures of the main components of air , oxygen 21% by volume and nitrogen approximately 79% by volume are: The minimum safe lower limit for
150-676: A particular gas in a mixture is the volume of one component of the gas mixture. It is useful in gas mixtures, e.g. air, to focus on one particular gas component, e.g. oxygen. It can be approximated both from partial pressure and molar fraction: V X = V t o t × p X p t o t = V t o t × n X n t o t {\displaystyle V_{\rm {X}}=V_{\rm {tot}}\times {\frac {p_{\rm {X}}}{p_{\rm {tot}}}}=V_{\rm {tot}}\times {\frac {n_{\rm {X}}}{n_{\rm {tot}}}}} Vapor pressure
180-396: A reversible reaction involving gas reactants and gas products, such as: a A + b B ↽ − − ⇀ c C + d D {\displaystyle {\ce {{{\mathit {a}}A}+{{\mathit {b}}B}<=>{{\mathit {c}}C}+{{\mathit {d}}D}}}}
210-458: A risk when these oxygen partial pressures and exposures are exceeded. The partial pressure of oxygen also determines the maximum operating depth of a gas mixture. Narcosis is a problem when breathing gases at high pressure. Typically, the maximum total partial pressure of narcotic gases used when planning for technical diving may be around 4.5 bar absolute, based on an equivalent narcotic depth of 35 metres (115 ft). The effect of
240-461: A toxic contaminant such as carbon monoxide in breathing gas is also related to the partial pressure when breathed. A mixture which may be relatively safe at the surface could be dangerously toxic at the maximum depth of a dive, or a tolerable level of carbon dioxide in the breathing loop of a diving rebreather may become intolerable within seconds during descent when the partial pressure rapidly increases, and could lead to panic or incapacitation of
270-452: Is ASTM G72. The time t ig {\displaystyle t_{\text{ig}}} it takes for a material to reach its autoignition temperature T ig {\displaystyle T_{\text{ig}}} when exposed to a heat flux q ″ {\displaystyle q''} is given by the following equation: where k = thermal conductivity , ρ = density, and c = specific heat capacity of
300-515: Is about 105 km (65 mi) east, is named in recognition of the coal found in the area, traditionally spelt "Paulatuuq" or "place of coal". 69°31′N 126°33′W / 69.517°N 126.550°W / 69.517; -126.550 Autoignition temperature The autoignition temperature or self-ignition temperature , often called spontaneous ignition temperature or minimum ignition temperature (or shortly ignition temperature ) and formerly also known as kindling point , of
330-495: Is also true in chemical reactions of gases in biology. For example, the necessary amount of oxygen for human respiration, and the amount that is toxic, is set by the partial pressure of oxygen alone. This is true across a very wide range of different concentrations of oxygen present in various inhaled breathing gases or dissolved in blood; consequently, mixture ratios, like that of breathable 20% oxygen and 80% Nitrogen, are determined by volume instead of by weight or mass. Furthermore,
SECTION 10
#1732852275548360-455: Is often called the normal boiling point . The higher the vapor pressure of a liquid at a given temperature, the lower the normal boiling point of the liquid. The vapor pressure chart displayed has graphs of the vapor pressures versus temperatures for a variety of liquids. As can be seen in the chart, the liquids with the highest vapor pressures have the lowest normal boiling points. For example, at any given temperature, methyl chloride has
390-496: Is quite often referred to as the Henry's law constant. Henry's law is sometimes written as: where k ′ {\displaystyle k'} is also referred to as the Henry's law constant. As can be seen by comparing equations ( 1 ) and ( 2 ) above, k ′ {\displaystyle k'} is the reciprocal of k {\displaystyle k} . Since both may be referred to as
420-431: Is the pressure of a vapor in equilibrium with its non-vapor phases (i.e., liquid or solid). Most often the term is used to describe a liquid 's tendency to evaporate . It is a measure of the tendency of molecules and atoms to escape from a liquid or a solid . A liquid's atmospheric pressure boiling point corresponds to the temperature at which its vapor pressure is equal to the surrounding atmospheric pressure and it
450-409: The equilibrium so as to favor either the right or left side of the reaction in accordance with Le Chatelier's Principle . However, the reaction kinetics may either oppose or enhance the equilibrium shift. In some cases, the reaction kinetics may be the overriding factor to consider. Gases will dissolve in liquids to an extent that is determined by the equilibrium between the undissolved gas and
480-435: The Henry's law constant, readers of the technical literature must be quite careful to note which version of the Henry's law equation is being used. Henry's law is an approximation that only applies for dilute, ideal solutions and for solutions where the liquid solvent does not react chemically with the gas being dissolved. In underwater diving the physiological effects of individual component gases of breathing gases are
510-427: The autoignition temperature for hydrocarbon/air mixtures decreases with increasing molecular mass and increasing chain length . The autoignition temperature is also higher for branched-chain hydrocarbons than for straight-chain hydrocarbons. Partial pressure In a mixture of gases , each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied
540-472: The entire volume of the original mixture at the same temperature . The total pressure of an ideal gas mixture is the sum of the partial pressures of the gases in the mixture ( Dalton's Law ). The partial pressure of a gas is a measure of thermodynamic activity of the gas's molecules . Gases dissolve, diffuse, and react according to their partial pressures but not according to their concentrations in gas mixtures or liquids. This general property of gases
570-422: The equilibrium constant of the reaction would be: K p = p C c p D d p A a p B b {\displaystyle K_{\mathrm {p} }={\frac {p_{C}^{c}\,p_{D}^{d}}{p_{A}^{a}\,p_{B}^{b}}}} For reversible reactions, changes in the total pressure, temperature or reactant concentrations will shift
600-697: The fact that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the individual gases in the mixture. This equality arises from the fact that in an ideal gas, the molecules are so far apart that they do not interact with each other. Most actual real-world gases come very close to this ideal. For example, given an ideal gas mixture of nitrogen (N 2 ), hydrogen (H 2 ) and ammonia (NH 3 ): p = p N 2 + p H 2 + p NH 3 {\displaystyle p=p_{{\ce {N2}}}+p_{{\ce {H2}}}+p_{{\ce {NH3}}}} where: Ideally
630-401: The following isotherm relation: V X V t o t = p X p t o t = n X n t o t {\displaystyle {\frac {V_{\rm {X}}}{V_{\rm {tot}}}}={\frac {p_{\rm {X}}}{p_{\rm {tot}}}}={\frac {n_{\rm {X}}}{n_{\rm {tot}}}}} The partial volume of
SECTION 20
#1732852275548660-417: The gas that has dissolved in the liquid (called the solvent ). The equilibrium constant for that equilibrium is: where: The form of the equilibrium constant shows that the concentration of a solute gas in a solution is directly proportional to the partial pressure of that gas above the solution . This statement is known as Henry's law and the equilibrium constant k {\displaystyle k}
690-415: The highest vapor pressure of any of the liquids in the chart. It also has the lowest normal boiling point (−24.2 °C), which is where the vapor pressure curve of methyl chloride (the blue line) intersects the horizontal pressure line of one atmosphere ( atm ) of absolute vapor pressure. At higher altitudes, the atmospheric pressure is less than that at sea level, so boiling points of liquids are reduced. At
720-400: The material of interest, T 0 {\displaystyle T_{0}} is the initial temperature of the material (or the temperature of the bulk material). Temperatures vary widely in the literature and should only be used as estimates. Factors that may cause variation include partial pressure of oxygen, altitude, humidity, and amount of time required for ignition. Generally
750-424: The partial pressure of an individual gas component in an ideal gas can be obtained using this expression: p i = x i ⋅ p {\displaystyle p_{\mathrm {i} }=x_{\mathrm {i} }\cdot p} The mole fraction of a gas component in a gas mixture is equal to the volumetric fraction of that component in a gas mixture. The ratio of partial pressures relies on
780-451: The partial pressures of oxygen and carbon dioxide are important parameters in tests of arterial blood gases . That said, these pressures can also be measured in, for example, cerebrospinal fluid . The symbol for pressure is usually p or pp which may use a subscript to identify the pressure, and gas species are also referred to by subscript. When combined, these subscripts are applied recursively. Examples: Dalton's law expresses
810-602: The partial pressures of oxygen in a breathing gas mixture for diving is 0.16 bars (16 kPa) absolute. Hypoxia and sudden unconsciousness can become a problem with an oxygen partial pressure of less than 0.16 bar absolute. Oxygen toxicity , involving convulsions, becomes a problem when oxygen partial pressure is too high. The NOAA Diving Manual recommends a maximum single exposure of 45 minutes at 1.6 bar absolute, of 120 minutes at 1.5 bar absolute, of 150 minutes at 1.4 bar absolute, of 180 minutes at 1.3 bar absolute and of 210 minutes at 1.2 bar absolute. Oxygen toxicity becomes
840-480: The ponds are characteristic of acidic environments worldwide, in contrast to the typically Arctic biota in adjacent alkaline ponds. Although the soil of the region contains much limestone , the buffer effect has completely disappeared. Weathering of the coastline of the area leads to the continuous exposure of new mineral deposits from the muds that make up the underlying geology. These are typically colored red when iron-rich. The nearest community, Paulatuk , which
870-559: The ratio of partial pressures equals the ratio of the number of molecules. That is, the mole fraction x i {\displaystyle x_{\mathrm {i} }} of an individual gas component in an ideal gas mixture can be expressed in terms of the component's partial pressure or the moles of the component: x i = p i p = n i n {\displaystyle x_{\mathrm {i} }={\frac {p_{\mathrm {i} }}{p}}={\frac {n_{\mathrm {i} }}{n}}} and
900-413: The top of Mount Everest , the atmospheric pressure is approximately 0.333 atm, so by using the graph, the boiling point of diethyl ether would be approximately 7.5 °C versus 34.6 °C at sea level (1 atm). It is possible to work out the equilibrium constant for a chemical reaction involving a mixture of gases given the partial pressure of each gas and the overall reaction formula. For
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