8.8 - Gases. These are assumptions that can be made about 99% of the gases we come in contact with which are called ideal gases.

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1 Gases The substance that we come in contact with every second of every day is in fact the substance we never think about. This substance is a mixture of gases known as the atmosphere. Gases have the weakest intermolecular attractions and are therefore in this state of matter that is not readily in our thoughts. This weak intermolecular force is called London Dispersion Forces. London Dispersion Forces These attractions arise in all nonpolar substances because of temporary, instantaneous dipoles created by electrons in a substance. Every substance has London Dispersion Forces present since all substances have some amount of electrons. But substances such as many of the diatomic molecules H 2, N 2, O 2, F 2, and Cl 2 as well as other nonpolar gases such as the noble gases and CO 2 (carbon dioxide), CH 4 (methane), and C 3 H 8 (propane) are all dispersion forces. Due to only instantaneous attractions, these substances will have a very low boiling point. Kinetic Molecular Theory of Gases These are assumptions that can be made about 99% of the gases we come in contact with which are called ideal gases. Gas molecules are moving in rapid, random motion with high kinetic energy Gas molecules essentially have no volume Gas molecules essentially have no intermolecular attractions Gas molecules exhibit elastic collisions or do not lose energy when they collide) Gas Laws Boyle s Law The pressure of a gas and the volume of a gas are inversely proportional. P 1 V 1 = P 2 V 2 Example: If a sample of neon gas is at 2 atm with a volume of 4 L. If the volume is changed to 1 L, what is the new pressure? Answer: 8 atm. If the volume decreases by a factor of 4 (divides by 4), then the pressure will increase by a factor of 4 (multiply by 4). 2 atm x 4 = 8 atm Charles Law The volume of a gas and the absolute temperature of a gas is directly proportional. V 1 T 1 = V 2 T 2

2 Example: A sample of nitrogen gas has a volume of 5 L and is at 200 K. If the temperature increases to 1000 K, what is the new volume? Answer: 25 L. If the temperature increased by a factor of 5 (multiplies by 5), then the volume increases by a factor of 5 (multiplies by 5). 5 L x 5 = 25 L Lussac s Law The pressure of a gas and the absolute temperature of a gas is directly proportional. P 1 T 1 = P 2 T 2 Example: A sample of helium gas has a pressure of 6 atm and is at 200 K. If the temperature decreases to 100 K, what is the new pressure? Answer: 3 atm. If the temperature decreased by a factor of 2 (divides by 2), then the pressure decreases by a factor of 2 (divides by 2). 6 atm / 2 = 3 atm Factors of a Gas Pressure Gas pressure is caused by the collisions of the gas particles with each other and the sides of the container. Temperature Gas temperature is caused by the average kinetic energy of the particles. Volume Gas volume is caused by the size of the container. Moles Gas moles is caused by the amount of particles. Example Explain Boyle s Law using a molecular view of the factors of a gas. Answer When the amount of gas particles (moles) and average kinetic energy (temperature) of a gas is held constant, when the volume of the container (volume) decreases, the gas particles exhibit more collisions with the sides of the container and therefore the pressure increases.

3 Atmosphere Composition of the Atmosphere The atmosphere is largely made up of nitrogen gas (N 2 ) and oxygen gas (O 2 ). Layers of the Atmosphere

4 Scientists divide the Earth s atmosphere into four main layers classified according to changes in temperature. The four layers are the: Troposphere The layer of the atmosphere in which Earth s weather occurs. Tropo- means turning or changing and this layer contains almost all of the mass of the atmosphere. Every 1 kilometer increase in altitude changes the air approximately 6.5 degrees Celsius cooler. Stratosphere This second layer of the atmosphere contains the ozone (O 3 ) layer. The ozone layer is important since it protects Earth s living things from the dangerous ultraviolet radiation from the sun. The chemical reaction for the conversion of ozone is 2 O 3 (g) 3 O 2 (g). Strato- means layer or spread out. While the lower stratosphere is cold (about -60 degrees Celsius), the upper stratosphere is warmer due to the absorbed heat from the UV radiation. Mesosphere A drop in temperature marks the beginning of the meso- or middle layer. This layer protects Earth s surface from being hit by most meteoroids. Thermosphere The outermost layer of the atmosphere, this extends from 80 kilometers above Earth s surface into space. The air is very thin (0.001% as dense as air at sea level), but very hot, up to 1,800 degrees Celsius. This is because sunlight strike the thermosphere first. Nitrogen and oxygen molecules convert this energy into heat. Although the temperature is very hot due to the kinetic energy of the molecules, there are not enough molecules to make the measured temperature any higher than 0 degrees Celsius. The thermosphere is divided into two layers: Ionosphere The lower layer where the energy from the sun causes gas molecules to become electrically charged particles called ions. The Northern Light (Aurora Borealis) are where these particles are also attracted by the Earth s magnetic field. Exosphere The outer layer of the thermosphere that extends into space. Air Quality Pollutants are harmful substances in the air, water, or soil. Air that contains harmful particles and gases is said to be polluted. Sources of Pollution Natural Sources Forest fires, soil erosion, and dust storms release a great deal of smoke and dust into the air. Particles of mold and pollen as well as erupting volcanoes are all natural sources of pollution. Human Activity Construction and farming can send soil and dust into the air but most air pollution come from the burning of fossil fuels such as coal, oil, gasoline, and diesel fuel. Almost half the pollution comes from cars and motor vehicles as well as factories and plants. All fossil fuels contain hydrocarbons (C x H y ) and when burned with O 2 can produce a variety of pollutants.

5 Pollutant Chemical Compounds The following are examples of the chemical compounds of pollutants: Ozone (O 3 ) A major part of smog that is found in the troposphere. It can lead to frequent asthma attacks, breathing problems, and eye irritation. Light/Heat + NO 2 + VOCs O 3 NO 2 comes from vehicles, fuel combustion, and industry and VOCs are volatile organic compounds from fuel combustion. Carbon Monoxide (CO) A gas that comes from the incomplete burning of fossil fuels, mostly in cars that cannot be seen or smelled. It reduced the ability of blood to deliver oxygen to the cells and in high concentrations can be fatal. C x H y + limited O 2 CO + H 2 O Nitrogen Monoxide (NO) and Nitrogen Dioxide (NO 2 ) These two pollutants are jointly referred to as NO x. Nitrogen dioxide is a reddish-brown gas that comes from the burning of fossil fuels and has a strong smell. High levels can result in breathing problems, lung damage. This reacts in the atmosphere to form acid rain, which can harm plants and animals. O 2 + N 2 2 NO 2 NO + O 2 2 NO 2 Sulfur Dioxide (SO 2 ) A corrosive gas that cannot be seen or smelled at low levels but can have a rotten egg smell at high levels. It can result in breathing problems and lung damage. S + O 2 SO 2 Combustion Reaction to Form Pollutants Formation of Acid Rain VOCs + O 2 NO x + CO 2 + CO + SO 2 + O 3 Nitrogen oxides and sulfur oxides (non-metal oxides) react with the water in the air to form acid compounds, nitric acid (HNO 3 ) and sulfuric acid (H 2 SO 4 ), respectively. Acid Rain Reactions Result of Acid Rain 3 NO 2 + H 2 O 2 HNO 3 + NO SO 3 + H 2 O H 2 SO 4 Acid rain can damage buildings and statues made of calcium carbonate. See reaction below: CaCO 3 (s) + 2 HNO 3 (aq) Ca(NO 3 ) 2 (aq) + H 2 O (l) + CO 2 (g) It can also harm lakes and ponds and make water so acidic that plants, amphibians, fish, and insects can no longer survive in it. The map below shows the acid rain ph measurements in the United States. The lower the ph, the greater the acidic rain which is closer to the red on the map. The green places on the map indicates less acid rain content.

6 Carbon and Oxygen Cycles Producers, consumers, and decomposers all play roles in recycling carbon and oxygen in ecosystems. This cycle involves four processes: Photosynthesis: Green plants and tress perform the following chemical reaction: CO 2 + H 2 O + light energy C 6 H 12 O 6 + O 2 Cellular Respiration: Animals take in simple sugars according to the following chemical reaction: C 6 H 12 O 6 + O 2 CO 2 + H 2 O + release energy Combustion: Natural combustion and combustion of fossil fuels according to the following reaction: C x H y + O 2 CO 2 + H 2 O Decomposition: Organic matter (plants, animals) decompose, often with the aid of bacteria (decomposers) to return carbon, oxygen, nitrogen, water, and calcium to the environment.

Nitrogen Cycle Most organisms can use nitrogen only once it has been fixed, or combined with other elements to form nitrogen-containing compounds.

This is done through lightning or by certain kinds of bacteria. Once nitrogen is fixed, producers can use it to build proteins and other complex compounds.

7 Nitrogen Cycle Most organisms can use nitrogen only once it has been fixed, or combined with other elements to form nitrogen-containing compounds. The process of changing free nitrogen into a usable form of nitrogen is called nitrogen fixation. This is done through lightning or by certain kinds of bacteria. Once nitrogen is fixed, producers can use it to build proteins and other complex compounds. Decomposers, in turn, break down these complex compounds in animal wastes and the bodies of dead organisms where nitrogen compounds are returned to the soil. It is often in cycle many times before returning to the air.

Guided Reading Chapter 16: The Atmosphere

Name Number Date Guided Reading Chapter 16: The Atmosphere Section 16-1: The Air Around You 1. The condition of Earth s atmosphere at a particular time and place is called 2. How does Earth s atmosphere