Physical Structure of Water & Its Properties PDF

Physical structure of water & its properties Dr. Aly El-Hadidy 2021/2022  Water statistics Covers 75% of Earth’s surface 97% oceans 3% freshwater 2% (of Total) in ice caps and glaciers 1% in lakes, underground, or in...

Physical structure of water & its properties Dr. Aly El-Hadidy 2021/2022  Water statistics Covers 75% of Earth’s surface 97% oceans 3% freshwater 2% (of Total) in ice caps and glaciers 1% in lakes, underground, or in atmosphere (usable by humans) Makes up 70% of the human body 92% of blood plasma 80% of muscle tissues 60% of red blood cells Molecular Structure of Water Water is formed when two hydrogen atoms bond to one oxygen atom by a covalent bond. Water molecule is not symmetrical and has a shape like a widened “V” Electrons spend more time near the (O) and less time near the (H)  Polarity of Water The oxygen atom is much larger than the hydrogen atoms so it tends to “share” the electrons a little more than the hydrogen atoms Because oxygen is more electronegative, the region around oxygen has a partial negative charge and the region near the two hydrogen atoms has a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.  Hydrogen bonds The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond.  Hydrogen bonds Hold water molecules together Each water molecule can form a maximum of 4 hydrogen bonds The hydrogen bonds joining water molecules are weak, about 1/20th as strong as covalent bonds. They form, break, and reform with great frequency It provides water with its extraordinary properties Properties of water  Cohesion It is the attraction between water molecules to each other through Hydrogen bonds (H) The cohesion of water molecules leads to two other important properties: 1. Surface Tension the attraction between water molecules at the surface of the liquid 2. High Specific Heat it takes a lot of energy to warm up water and it takes a very long time for warm water to cool off 3. Viscosity  Surface Tension Resistance of a liquid to an increase in surface area because H bonds in H2O Ex: floating a paper clip Next to mercury, water has the highest surface tension of all liquids. because hydrogen bonds among surface water molecules resist stretching or breaking the surface. Water behaves as if covered by an invisible film. Some animals can stand, walk, or run on water without breaking the  Adhesion The attraction of water to other surfaces/substances The adhesion of water leads to two other important properties: 1. Water as a “universal” solvent Water only dissolves polar molecules 2. Capillary action Universal Solvent Solvent: is the substance that dissolves other substances. Water is an excellent solvent because of its hydrogen bonds Since water can dissolve more things than any other natural substance, it is known as the “ Universal Solvent” Properties of Solvents : 1. Interacts with other polar compounds 2. Is repelled by non-polar compounds 3. Small size allows it to saturate areas 4. Can convey other substances in solutions  When salt is placed in water, the strongly charged salt ions attract to the weaker charged water molecules. Water molecules surround each ion. Salt crystals fall apart, or dissociates, and the salt dissolves. Gases such as oxygen, carbon dioxide, and nitrogen are also easily dissolved into water Capillary Action Water is able to “climb” objects against the forces of gravity Wettable surfaces cause a film of water to partially pull away from other water molecules and cling to the surface. Capillary action is important in soil and plant/water relations.  Diffusion The tendency of substances to move from areas of high concentration to areas of low concentration Osmosis Osmosis is the net movement of water across a selectively permeable membrane driven by a difference in solute concentrations on the two sides of the membrane The water moves from the area of low solute concentration to the area of high solute concentration until equilibrium is reached Heat effect on water density As the amount of heat decrease the kinetic energy decreases and so the molecules come closer to each other So water and Most liquids become more dense as you cool them. At temperature 4oC and lower , water actually becomes slightly less dense. why? This is due to the way that water molecules “line up” as the water molecules begin to repel each other as they come very close together Water “organizing” with H bonds as it freezes. Forms hexagon shapes. What is Temperature? A measure of the average kinetic energy of the particles in a sample of matter, expressed in terms of units or degrees designated on a standard scale oC oF K Steam point 373 100o 212o The relationships of 100 K 100 Co 180 Fo the temperature Ice point 273 0o 32o scales Absolute zero 0o -273o -460o Zeroth law of thermodynamics Two systems are in thermal equilibrium only if they have the same temperature. Two systems each in thermal equilibrium with a third system are in thermal equilibrium with each other. A B C Heat is Defined as Energy Heat is the thermal energy that is absorbed or given up. Unit of heat is calorie (1 cal) is the quantity of heat required to raise the temperature of 1 g of water by 1 C0. For any enclosed system the amount of heat lost is equal to the amount of heat gained.  Conservation of Energy For any enclosed system. Whenever there is a transfer of heat within a system, the heat lost by the warmer bodies must equal the heat gained by the cooler bodies (Heat Lost) = (Heat Gained) m1 C1 Δt1 = m2 C2 Δt2 Heat Capacity It is the amount of heat required to raise the temperature of whole the body by a unit degree. Specific Heat Capacity (C) It is the quantity of heat (Q) needed to raise the temperature (t) of a unit mass (m) by a unit degree. Q c ; Q  mct m t C unit is cal/g C0  Change of Phase When a change of phase occurs, there is only a change in potential energy of the molecules. The temperature is constant during the change. The quantity of heat Q required change the phase of substance is given as Q = m L The latent heat of (L) Liquid Vaporization Solid Gas is the quantity of heat per unit mass fusion required to change the substance from one phase to another phase. Q = mLf Q = mLv L = Q /m Fusion, vaporization, condensation, latent heats, evaporation, freezing point, melting point. cice= 0.5 cal/gC0 cwater= 1 cal/gC0 temperature t m c3 Δt m Lv 1000C m c2 Δt steam steam and m Lf water 00C water m c1 Δt ice and water ice Q Hydrotherapy Hydrotherapy is a method of treating disease by using water at different temperatures and in different ways. The term (Hydrotherapy)encompasses a broad range of approaches and therapeutic methods that take advantage of the physical properties of water, such as temperature and pressure, for therapeutic purposes, to stimulate blood circulation and treat the symptoms of certain diseases. Hydrotherapy water has certain physical properties which include weight, Specific gravity, density, viscosity, buoyancy, Hydrostatic pressure, surface tension and specific heat /thermal energy transfer. The most important physical laws of water that physiotherapist should understand and apply when giving hydrotherapy, are buoyancy and hydrostatic pressure. Therapeutic uses of hydrotherapy Superficial heating and cooling Wound care Water exercise Pain control Edema control  Benefits of Water Therapy Water therapy provides little to no impact, unlike exercises done on land Even if you are unable to stand on land because of an injury or due to pain, you will be able to stand in the water Water makes everyone equal, meaning that there are no limitations based on age, body size, sex, or health conditions Water is incredibly supportive of the body When performing exercises in water, there is a limited chance of falling Water is full of healing properties, which will help help remedy injuries much quicker than other forms of therapy Water works to reduce swelling in joints All exercises performed in the water use the total body You will not be sore or experience any stiffness following a water therapy session Turbulence in the water provides you with a body massage as you are going through the motions You will work harder to move your limbs in the water due to resistance Due to the resistance of water, your movements will be slower and more precise The use of your muscles in the water is more efficient Water therapy is great for back pain, as it does not have as big of an impact on the spine Warmth, buoyancy, and support of water provides a safe environment, especially for those with balance problems QUIZ (1) Problem 1: A 500 g copper coffee mug is filled with 200g of coffee. How much heat was required to heat cup and coffee from 20 to 960C? Problem 2: A handful of copper shot is heated to 900C and then dropped into 80 g of water in an insulated cup at 100C. If the equilibrium temperature is 180C, what was the mass of the copper? Problem 3: How much heat is needed to convert 10 g of ice at -200C to steam at 1000C? Problem 4: How many grams of ice at 00C must be mixed with four grams of steam at 1000C in order to produce water at 600C?