15.1 Liquid Water and its Properties Chapter 15: Water and Aqueous Systems Part 1 15.1 Liquid Water and its Properties Why do we care about water? 3/4 of earths surface, 60% of our body weight Unique properties make life possible

Water Molecule Warm-up Draw your water molecule in the space provided. Label the hydrogen and oxygen on your water molecule. Describe what happens when your water molecule is brought near the water molecule of someone near you. Draw a picture of three water molecules interacting in the space provided.

Water Molecule Water has polar bonds due to a difference in electronegativity of 1.4. Water is a polar molecule and has a bent shape due to lone pair electrons on the central element, oxygen O: 3.5 H:2.1 How polar is it? Address angle

Question! Draw a water molecule and label its negative and positive ends.

Water Molecule Molecules are attracted to each other by hydrogen bonds ∂- Polar Covalent bond O ∂+ H H Remember ∂ means partial or slightly. Intermolecular vs. Intramolecular ∂- O H H Hydrogen bond ∂+

Surface Tension The inward force, or pull, that tends to minimize the surface area of a liquid Tends to hold a drop of liquid in a spherical shape A sphere has the smallest surface area for a given volume Skin like properties (waterstrider) Surface molecules attracted to each other through H-bonding and can’t h-bond to air H-bonding is the reason for water beading up Cohesion-attraction of water to water (surface tension) Adhesion -attraction of water to non water (water sticking to a surface)

Question! Draw arrows showing the pull of surface tension on the drop of water below.

Surface Tension Water’s surface tension is stronger than most liquids reduces vapor pressure Define vapor pressure, h-bonds hold liquid together, h-bonds must break to increase vapor pressure

Surface Tension Surfactant – substance that interferes with the hydrogen bonds between water molecules. Surface tension breaks down and the water spreads out. Surface active agent Why we use soap Decreases surface tension

Soaps & Detergents Soaps and detergents are chains that have one end that is like oil and has no charge and the other end is charged. SO4- SO4- SO4- SO4- SO4- SO4- O O Oil droplet O O O O

Thermochemistry Review Specific heat capacity – the amount of energy required to raise the temperature of 1.0 g of water by 1C. q = m  C  T C = specific heat capacity 1.00 cal/g°C or 4.18 J/g°C m = mass of substance in grams ∆T = change in temperature in °C q = heat in joules or calories Thermochem properties of water are incredibly important

Question! Why would a burn from steam at 100C be worse than a burn from water at 100C?

Impact of Thermochemical Properties Water allows for more temperate climates. Water cools more slowly at night and heats more slowly during the day reducing temp variations

15.1 Water Vapor & Ice

Water Vapor Evaporation – the change of state from liquid to gas at the surface of a liquid that is not boiling Ever left a glass out over night? Endothermic- ex: sweat, Rubbing alcohol (colder because evap is faster, less h-bonds)

Water Vapor Condensation – the change of state from a gas to a liquid Water has a high heat of vaporization (2260 J/g) 2260 J of energy are needed to change 1.0 g of water from a liquid to a gas or a gas to a liquid Water’s high boiling and melting points are caused by hydrogen bonding. When compared to ammonia (NH3) the hydrogen bonds are stronger. It takes more energy to disrupt these bonds, giving water a higher boiling and melting point. Breathing on a cold day A cold glass sweating Exothermic Where does the water come from that condenses on the cup? In the breath?

The Heating Curve! 2260 J/g more heat in steam than liquid

Ice Freezing – the change of state from a liquid to a solid Water has a high heat of fusion (334 J/g) 334 J of energy is needed to change 1.0 g of water from a solid to a liquid or a liquid to a solid

Ice Density – the ratio of the mass of an object to its volume M D = V

Question! What happens when water freezes?

Ice What are some benefits of ice floating? Insulates fish in winter, ground & air cold, ice keeps water warm, like eskimos

Review Problems = (225g)(4.18 J/gºC)(36ºC) = 33900 J Calculate the heat released when a cup of tea cools from 61C to 25C. The mass of the tea is 225g. (Assume the specific heat of the tea is equivalent to that of water) Givens: q = mCT C = 4.18 J/g°C m = 225 g ∆T = 61°C - 25°C = 36°C q = ? = (225g)(4.18 J/gºC)(36ºC) Variables, formular, plug in, solve, units, sig digs = 33900 J

Review problems Calculate the amount of heat needed to boil (vaporize) a kettle filled with water (250 g). Given: phase change, so DA only m = 250g Hvap= 2260 J/g q = ? 250g 2260 J = 1 g q = 565,000 J Assume water is already at 100°C

Review Problems How much heat energy is needed to melt 30.0 g of ice at 0C to water at 80C? Givens: Heat change and phase change C = 4.18 J/g°C Hfus= 334 J/g m = 30.0 g ∆T = 80°C - 0°C = 80°C q = ? To melt, use DA 30.0 g 334J = 1.00 x 104 J 1 g To heat, use q = mCΔT q = (30.0g)(4.18J/gºC)(80ºC) = 1x104 J Total = 2.0 x 104J T when there is temp change, no temp change during phase change

Review Which atom in the water molecule is most electronegative? Hydrogen Oxygen Neither How are water molecules held together? magic dispersion forces covalent bonds hydrogen bonds

Review Water has a ________________ vapor pressure due to _________________. low; low surface tension high; london dispersion forces low; hydrogen bonds high; hydrogen bonds Water has a ____________ heat capacity and a ______________ heat of vaporization. high; low high; high low; high low; low

Review Due to the high heat capacity and vaporization energy of H2O, coastal areas have ___ temperatures. moderate extreme low high Which of the following are characteristics of surface tension? reduces vapor pressure holds liquids in spherical shapes is caused by hydrogen bonding is very strong in water all of the above

Review A surfactant is a substance that interferes with ________________ and decreases the _________________. free time; productivity hydrogen bonding; surface tension intramolecular forces; vapor pressure