Polar And Nonpolar Compounds, Polarity Objective: Fill & Download for Free

Water can boil at room temperature. I have seen it. And as it boils, the temperature drops. We typically see boiling when we heat up liquids on our stove tops. So we naturally associate boiling with a higher temperature and we do not consider boiling as a means of cooling an object down but that is what happens.Evaporation and boiling both cool a substance. Why is that the case and why do we not observe it? Well for both of these processes, the higher energy particles are the first to leave the liquid and escape as a gas. This cools down the liquid because all temperature really is is the average kinetic energy of all the particles in a sample. So as the sample boils or evaporates, the kinetic energy declines and by definition the temperature drops.How do we make a substance boil? Well every molecule has some form of attraction for another molecule. This attraction is weak for nonpolar compounds and stronger for polar compounds (this is a whole lesson in itself). Water forms very strong attractions to other water molecules because of its strong partial positive and negative sides attracting. Think of magnets attracting other magnets. This means they are harder to separate. Then you look at nitrogen. Nitrogen is very weakly attracted to other nitrogen by comparison to water. Now understanding these attractions is very important for understanding why things are in the state of matter that they are in. To build onto this, all molecules are in motion. The weaker the attraction mentioned earlier, the easier they can move around each other. This leads to a “vapor pressure” which is the pressure that a liquid exerts on its surroundings as it tries to become a gas from all that motion. In the case of water, that vapor pressure is fairly low. In the case of nitrogen, it is fairly high. And this is once again because water is more strongly attracted to other water molecules than nitrogen is to other nitrogen molecules. Stronger vapor pressures lead to compounds becoming vapor with more ease.So how does this tie into temperature? By increasing the temperature of the liquid, you are by definition increasing the kinetic energy of the liquid. This increase in motion increases vapor pressure and speeds up evaporation. Because we are adding energy (like on a stove top), we never notice the drop in energy (temperature) from the process of evaporation or boiling.How do we make liquids (like water) boil at even lower temperatures? Like I mentioned before, the liquid is exerting an upwards pressure called vapor pressure. There is additionally a pressure pushing down on the liquid typically called atmospheric pressure. In the case of water, atmospheric pressure is stronger than vapor pressure at room temperature. This is why no boiling occurs in that glass of water you left on the counter top. For boiling to occur, vapor pressure must have reached the pressure pushing down on the liquid. This should lead to a question. What happens if the pressure being pushed down on the liquid is decreased like in a vacuum? The liquid may boil at lower temperatures.And what happens to the temperature when you aren’t adding thermal energy? The temperature will drop as the liquid boils away. This can actually lead to an incredible occurrence called the triple point. Eventually the kinetic energy will drop to the point where a solid begins to form. Yes, boiling can lead to freezing. This is the triple point. You will witness a solid, liquid, and gas at the same time or oscillating between the three from the same sample. Boiling drops temperature, liquid becomes a solid, the solid warms up a degree and becomes a liquid, which boils, etc. There are numerous videos on youtube that I would definitely check out.So back to your question, “Why is water hot when it boils and Liquid nitrogen cold when it boils?” It is that way because you are boiling them at atmospheric pressure and these are the relative temperatures needed to bring the vapor pressure to or above that downward pressure from the atmosphere

The physics of hydrophobicity can be simply understood as a procedure of minimisation system energy. There are three kinds of interface when two fluids are in contact with a solid surface, i.e. fluid1-solid, fluid2-solid and fluid1-fluid2. Higher energy interface tends to be replaced by a lower energy one. Then an equilibrium state is defined by a contact angle, which is determined by the well-known Young-Dupree equation for an idea smooth solid surface, at the three-phase contact line.Hydrophobicity can be categorised (based on apparent contact angle) into super-hydrophilic, hydrophilic (contact angle <90deg), hydrophobic (contact angle >90deg) and super-hydrohpobic (high contact angle + low contact angle hysteresis). Lotus leaf shows a super-hydrophobic property with water. This lotus effect is a combination of chemically hydrophobicity (wax component on leaf) and physical patterns (micro- and nano-protrusions on leaf structure). Air (which is also very hydrophobic, contact angle 180deg) is trapped under water droplet and between these micro-/nano-patterns. Consequently, wax layers and trapped air induce really high contact angle (~160deg) of water droplet on lotus leafIt refers to interaction of the object with water (hydro-). If energy of interaction of the object molecules with water is greater than inner energy of mutual interaction of the object molecules between them the the object is hydrophilic one. And it is hydrophobic in opposite caseIn chemistry, hydrophobicity is the physical property of a molecule (known as a hydrophobe) that is seemingly repelled from a mass of water.[1](Strictly speaking, there is no repulsive force involved; it is an absence of attraction.) In contrast, hydrophiles are attracted to water.Hydrophobic molecules tend to be nonpolar and, thus, prefer other neutral molecules and nonpolar solvents. Because water molecules are polar, hydrophobes do not dissolve well among them. Hydrophobic molecules in water often cluster together, forming micelles. Water on hydrophobic surfaces will exhibit a high contact angle.Examples of hydrophobic molecules include the alkanes, oils, fats, and greasy substances in general. Hydrophobic materials are used for oil removal from water, the management of oil spills, and chemical separation processes to remove non-polar substances from polar compounds.[2]Hydrophobic is often used interchangeably with lipophilic, "fat-loving". However, the two terms are not synonymous. While hydrophobic substances are usually lipophilic, there are exceptions, such as the silicones and fluorocarbons.The term hydrophobe comes from the Ancient Greek ὑδρόφόβος (hýdrophóbos), "having a horror of water", constructed from Ancient Greek ὕδωρ (húdōr), meaning 'water', and Ancient Greek φόβος (phóbos), meaning 'fear'.[3In 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gaswhereInterfacial tension between the solid and gas= Interfacial tension between the solid and liquid{\displaystyle \gamma _{\text{LG}}\ } = Interfacial tension between the liquid and gasθ can be measured using a contact angle goniometer.Wenzel determined that when the liquid is in intimate contact with a microstructured surface, θ will change to θW*{\displaystyle \cos \theta _{W}*=r\cos \theta \,}where r is the ratio of the actual area to the projected area.[8]Wenzel's equation shows that microstructuring a surface amplifies the natural tendency of the surface. A hydrophobic surface (one that has an original contact angle greater than 90°) becomes more hydrophobic when microstructured – its new contact angle becomes greater than the original. However, a hydrophilic surface (one that has an original contact angle less than 90°) becomes more hydrophilic when microstructured – its new contact angle becomes less than the original.[9]Cassie and Baxter found that if the liquid is suspended on the tops of microstructures, θ will change to θCB*:{\displaystyle \cos \theta _{\text{CB}}*=\varphi (\cos \theta +1)-1\,}where φ is the area fraction of the solid that touches the liquid.[10]Liquid in the Cassie–Baxter state is more mobile than in the Wenzel state.We can predict whether the Wenzel or Cassie–Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the smaller new contact angle is the state most likely to exist. Stated in mathematical terms, for the Cassie–Baxter state to exist, the following inequality must be true.[11]{\displaystyle \cos \theta >{\frac {\varphi -1}{r-\varphi }}}A recent alternative criterion for the Cassie–Baxter state asserts that the Cassie–Baxter state exists when the following 2 criteria are met:1) Contact line forces overcome body forces of unsupported droplet weight and 2) The microstructures are tall enough to prevent the liquid that bridges microstructures from touching the base of the microstructures.[12]A new criterion for the switch between Wenzel and Cassie-Baxter states has been developed recently based on surface roughness and surface energy.[13]The criterion focuses on the air-trapping capability under liquid droplets on rough surfaces, which could tell whether Wenzel's model or Cassie-Baxter's model should be used for certain combination of surface roughness and energy.Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slide angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity.[14]When a pipette injects a liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly advances outward. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle. The receding contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly recedes inward. The contact angle the droplet had immediately before receding inward is termed the receding contact angle. The difference between advancing and receding contact angles is termed contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.[how?]Surfaces that are not homogeneous will have domains that impede motion of the contact line. The slide angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie–Baxter state exhibit lower slide angles and contact angle hysteresis than those in the Wenzel state

Hi Readers,A piece of info for you all to read and exploreWater as a Lubricant : Water as a Lubricant and Cushion, Water is a major component of many of the body’s lubricating fluids. Just as oil lubricates the hinge on a door, water in synovial fluid lubricates the actions of body joints, and water in pleural fluid helps the lungs expand and recoil with breathing.Watery fluids help keep food flowing through the digestive tract, and ensure that the movement of adjacent abdominal organs is friction free. Water also protects cells and organs from physical trauma, cushioning the brain within the skull, for example, and protecting the delicate nerve tissue of the eyes. Water cushions a developing fetus in the mother’s womb as well.Water as a Heat Sink : A heat sink is a substance or object that absorbs and dissipates heat but does not experience a corresponding increase in temperature.In the body, water absorbs the heat generated by chemical reactions without greatly increasing in temperature. Moreover, when the environmental temperature soars, the water stored in the body helps keep the body cool.This cooling effect happens as warm blood from the body’s core flows to the blood vessels just under the skin and is transferred to the environment. At the same time, sweat glands release warm water in sweat.As the water evaporates into the air, it carries away heat, and then the cooler blood from the periphery circulates back to the body core. Water as a Component of Liquid Mixtures A mixture is a combination of two or more substances, each of which maintains its own chemical identity.In other words, the constituent substances are not chemically bonded into a new, larger chemical compound. The concept is easy to imagine if you think of powdery substances such as flour and sugar; when you stir them together in a bowl, they obviously do not bond to form a new compound.The room air you breathe is a gaseous mixture, containing three discrete elements—nitrogen, oxygen, and argon—and one compound, carbon dioxide. There are three types of liquid mixtures, all of which contain water as a key component.These are solutions, colloids, and suspensions.For cells in the body to survive, they must be kept moist in a water-based liquid called a solution. In chemistry, a liquid solution consists of a solvent that dissolves a substance called a solute. An important characteristic of solutions is that they are homogeneous; that is, the solute molecules are distributed evenly throughout the solution.“If you were to stir a teaspoon of sugar into a glass of water”,the sugar would dissolve into sugar molecules separated by water molecules.The ratio of sugar to water in the left side of the glass would be the same as the ratio of sugar to water in the right side of the glass. If you were to add more sugar, the ratio of sugar to water would change, but the distribution—provided you had stirred well—would still be even.Water is considered the “universal solvent” and it is believed that life cannot exist without water because of this.Water is certainly the most abundant solvent in the body; essentially all of the body’s chemical reactions occur among compounds dissolved in water. Because water molecules are polar, with regions of positive and negative electrical charge, water readily dissolves ionic compounds and polar covalent compounds.Such compounds are referred to as hydrophilic, or “water-loving.” As mentioned above, sugar dissolves well in water.This is because sugar molecules contain regions of hydrogen-oxygen polar bonds, making it hydrophilic. Nonpolar molecules, which do not readily dissolve in water, are called hydrophobic, or “water-fearing.”Source : OpenStax BooksThanks for reading, Remember Readers are Leaders.