#### • Class 11 Physics Demo

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# at what temperature does water become a gas

Question:AND WHY?

Answers:Ethanol is a liquid at RT Propane is a gas at RT NaCl is a solid at RT These properties are all due to intermoleccular attractions between the molecules in the samples. In gases, molecules are all floating around seperate from one an other. They hardly interact with each other at all. In liquids, molecules are quite close to each other and are held together in a smaller volume then gases. The molecules do not have as much energy as gas molecules. For a molecules to go from liquid to gas phase you have to provide it with enough energy to break away from all the other molecules. In solid phase molecules are very close to each other and hardly move at all. To go from solid to liquid you have to provide enough energy for the molecules to break their attractive forces with each other enough to be able to move around more freely. Propane is a hydrocarbon and is a non-polar compound. There are only very weak attractive forces between 1 propane molecule and another propane molecule. Because of this there are only very small forces holding the molecules in a sample together, so it does not take very much energy for the molecules to be in the gas phase. RT is enough. Ethanol has a polar group on it (OH). Polar groups have a slightly positive and a slightly negative end. The positive and of one molecule is attracted to the negative end of another molecule. So they are held close to each other by these "intermolecular" forces. These forces are moderate in stranght. Because ethanol molecules are attracted to each other like this it takes quite a bit of energy from an individual molecule to break away from these attractions. So ethanol is a liquid at RT. NaCl is an ionic compound. It consists of a cation Na+ and anion Cl- Cations and anions are extremely attracted to each other. In solid NaCl the cations and anions are arranged in a crystal lattice structure with alternating cations and anions that are all very strongly attracted to each other. It takes a large amount of energy to provide enough energy for these bonds to break. For this reason NaCl is solid at RT.

Question:Does water actually change from a liquid to a solid at exactly 0 degrees Celsius/32 degrees F? Does it change from a liquid to a gas at exactly 212 degrees F/ 100 degrees Celsius?

Answers:Great question! Also correct! Also open-air boiling point of water is typically considered to be 100 C or 212 F, although pressure and a change in composition of the liquid may alter the boiling or freezing point of the liquid. If you were to take something (anything at all) and break it up into almost the smallest things you could, you d get molecules. Everything there is is made up of lots of little molecules. If the molecules are stuck together really tightly, then they re called a solid. The solid form of water is ice. This actually makes a lot of sense, because it certainly does seem like all the little parts of a solid (like ice) are stuck together very tightly. When you heat something up, it makes the molecules move faster. If you heat up a solid, it melts and becomes a liquid. In a liquid (like water), the molecules are still stuck together, but they can move around some. What actually happens is that the molecules are still sort of sticking together, but they re constantly breaking apart and sticking to different molecules. This also makes sense when you think about water. Water sort of sticks together, but it breaks apart /really/ easily. If you heat a liquid like water up even more (like if you put it in a pot on the stove), then the molecules will move around so fast that they can t even hold on to each other at all. When this happens, all of the molecules go flying apart and become a gas (like when you boil water to make steam). The process of heating up a liquid like water to make a gas like steam is called "evaporation." When you do the opposite and cool a gas down to make a liquid, then it s called "condensation." Hope this answers your question! -Jerry

Question:i am looking for PSI

Answers:The critical point of air is 132 Kelvin and 61 atmospheres. This means that at normal temperature of 20C or 292 Kelvin it is impossible to compress air to a liquid form - it remains a gas at ALL pressures. You can only compress it to a liquid once it is already below 132 Kelvin, and this will take 61 atmospheres pressure at that point.

Question:

Answers:The Atmosphere How is the atmosphere structured? The atmosphere consists of four distinct layers, which are seperated by a boundaries that end in the suffix "pause". There is a lot of information in the Earth Science Reference Tables page 14. Troposphere-This layer of the atmosphere is closest to the earth and 99% of all weather takes place here because most of the water vapor is located here. Stratosphere-This layer is above the troposphere and contains ozone, which is an important gas, because it absorbs cancer-causing ultra violet rays from the Sun. Mesosphere-This layer is above the stratosphere. Thermosphere-This is the uppermost layer of the atmosphere. Earth Science Reference Table page 14: How do we describe the present condition of the atmosphere? The present condition of the atmosphere is called WEATHER and it is described using observations of temperature, air pressure, humidity, wind, cloudiness and precipitation. What is temperature? Temperature is a measure of the average kinetic energy of the particles of a substance. In other words, the more molecules vibrate within a substance, the higher the temperature. Measurement - There are three scales that measure temperature: CELSIUS, FAHRENHEIT AND KELVIN scales. There is a conversion scale on page 13 of your ESRT. Maps - Meteorologists find it useful to map temperatures and they use lines to connect equal temperatures called Isotherms. What is air pressure and how is it used to predict the weather? Air Pressure - Air pressure is also called barometric or atmospheric pressure. By definition, it is the weight of the atmosphere pushing down on the earth. Barometer - A barometer is the instrument that measures air pressure and it uses units of millibars (mb) or inches of mercury (inches). Factors that affect air pressure: Temperature - As the temperature of the air increases, the air pressure decreases, which is an indirect relationship. Humidity - As the humidity of the air increases, the air pressure decreases, which is an indirect relationship. You might ask "WHY?": Humid air is lighter than dry air. When water vapor enters dry air, it does not squeeze in between the molecules of air. Instead, the water vapor pushes out many of the air's heaviest molecules like Nitrogen and Oxygen. In other words, lighter molecules of water vapor replace heavier molecules and the result is the air weighs less and therefore has less air pressure. High air pressure - means that the atmosphere is heavy at that location and from our notes above, you can conclude that the air is probably cool and dry (if you are not sure, see notes above). So, if the barometer indicates high pressure or rising air pressure, you can conclude that the weather will be cool and dry. Low air pressure - means that the atmosphere is not heavy at that location and from our notes above, you can conclude that the air is probably warm and humid (if you are not sure, see notes above). So, if the barometer indicates low pressure or falling air pressure, you can conclude that the weather will be warmer and humid. Maps - Meteorologists find it useful to map air pressure and they use lines to connect equal equal air pressures called Isobars