HW9

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Houston Community College *

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1401

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Chemistry

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Dec 6, 2023

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Chapter 17 1. What are the four common phases of matter? The four common phases of matter are solid, liquid, gas, and plasma. 3. What is evaporation Evaporation is the process by which a liquid, such as water, changes into a gas state at a temperature below its boiling point. It occurs at the surface of the liquid when the molecules gain enough kinetic energy to escape into the gas phase. 7. Why is a steam burn more damaging than a burn from boiling water at the same temperature? When water changes from a liquid to a gas (steam), it absorbs a significant amount of heat energy in the process. So, when steam comes into contact with your skin, it not only transfers heat due to its temperature but also releases the latent heat, causing more severe burns. 13. Distinguish between evaporation and boiling. Evaporation occurs at the liquid's surface, even at temperatures below the boiling point, while boiling happens throughout the liquid when it reaches its boiling point. 21. Why does increasing the temperature of a solid make it melt? Increasing the temperature of a solid makes it melt because heat adds energy to the solid, increasing the kinetic energy of its particles. At a certain temperature called the melting point, the particles have enough energy to break the intermolecular forces holding them in a solid arrangement. This allows the solid to transition into a liquid state, where the particles can move more freely. 27. Does a liquid release energy or absorb energy when it changes into a solid? When a liquid changes into a solid, it releases energy. This energy is typically released in the form of heat, and the process is known as freezing or solidification. 33. You can make rain in your kitchen. Put a cup of water in a Pyrex saucepan or a glass coffeemaker and heat it slowly over a low flame. When the water is warm, place a saucer filled with ice cubes on top of the container. As the water below is heated, droplets form at the bottom of the cold saucer and combine until they are large enough to fall, producing a steady “rainfall” as the water below is gently heated. How does this resemble, and how does it differ from, the way in which natural rain is formed? The process described with a cup of water, a saucer of ice cubes, and gentle heating in the kitchen resembles the way natural rain is formed in the sense that

both involve the phase transition from a liquid to a gas. In both cases, the water evaporates and turns into water vapor. However, there are key differences: Natural rain is formed by the evaporation of water from the Earth's surface (e.g., oceans, lakes, and rivers), followed by the condensation of water vapor in the atmosphere to form clouds. The water droplets in these clouds eventually combine and become heavy enough to fall as precipitation (rain). In the kitchen experiment, the water is evaporated directly from a container and condensed on the cold saucer, bypassing the complex atmospheric processes involved in natural rain formation. 35. Do as Dean Baird demonstrates in Photo 2 of the chapter-opening photos, or as the sketch shows, and suspend a heavy weight by copper wire over an ice cube. In a matter of minutes, the wire will be pulled through the ice. The ice will melt beneath the wire and refreeze above it, leaving a visible path if the ice is clear. This happens because the weight, in contact with the wire, transmits its temperature to the wire. The wire then conducts heat to the ice, causing it to melt directly beneath the wire. Once the ice melts, it refreezes above the wire, leaving a visible path if the ice is clear. This process is an example of heat conduction and the transfer of thermal energy from the wire to the ice, resulting in localized melting and refreezing. Chapter 18 1. What is the origin and meaning of the word thermodynamics? The word "thermodynamics" has its origin in Greek. "Thermo" means heat, and "dynamics" refers to motion or change. So, thermodynamics literally means the study of heat and its relationship to other forms of energy and the way energy affects matter. 3. By how much does the volume of gas at 0°C contract for each decrease in temperature of 1 Celsius degree when the pressure is held constant? The volume of a gas at 0°C contracts by approximately 1/273 of its original volume for each decrease in temperature of 1 Celsius degree when the pressure is held constant. 9. What is meant by a system? A "system" refers to a specific portion of the universe that is being studied or analyzed. can be a physical or conceptual region of space or a collection of matter and energy that is under investigation. 13. If work is done on a system, does the internal energy of the system increase or decrease? If work is done by a system, does the internal energy of the system increase or decrease? When work is done on a system, the internal energy of the system typically increases. Work is a form of energy transfer into the system. Conversely, when work

is done by a system, the internal energy of the system decreases as the system is expending energy to perform work. 17. What is a temperature inversion? A temperature inversion is a meteorological phenomenon in which there is a reversal of the normal temperature profile of the Earth's atmosphere. Instead of temperatures decreasing with altitude (as they typically do), they increase or remain relatively constant over a certain vertical region of the atmosphere. 21. What exactly is thermal pollution? The concept of thermal pollution is related to the undesirable release of heat into the environment, particularly when it has a negative impact. 29. What is the third law of thermodynamics? The third law of thermodynamics, also known as the Nernst heat theorem or the unattainability principle, states that as the temperature of a system approaches absolute zero (0 Kelvin), the entropy of the system approaches a minimum or constant value. In other words, it's impossible to reach absolute zero in a finite number of steps, and at absolute zero, the entropy of a perfectly ordered crystal is minimal. 35. What is the ideal efficiency of an automobile engine that operates between the temperatures 600°C and 320°C? (Why is your answer not 47%?) Efficiency = 1 - (T2 / T1) = 1-(320+273.15) / (600+273.15) *100 = 32.06% The efficiency is 32 % because the value of temperatures used have to be absolutes Chapter 19 1. What is a wiggle in time called? What do you call a wiggle in space and time? A wiggle in time is called a "vibration" or a "oscillation." A wiggle in both space and time is referred to as a "wave. 5. How does a sine curve relate to the wave description? A sine curve is often used to represent a wave. It is a mathematical curve that describes the variation of a wave's amplitude over time or space. 7. How many vibrations per second are represented in a radio wave of 101.7 MHz? In a radio wave of 101.7 MHz, there are 101.7 million vibrations (cycles) per second. 15. What is the superposition principle?

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The superposition principle in physics states that when two or more waves intersect or overlap in a medium, the resultant displacement at any point is the algebraic sum of the individual wave displacements. 21. Can the Doppler effect be observed with longitudinal waves, with transverse waves, or with both? The Doppler effect can be observed with both longitudinal waves and transverse waves. 29. Tie a rubber tube, a spring, or a rope to a fixed support and produce standing waves. See how many nodes you can produce. I was able to produce 3 nodes when I tied a yellow wire to a fixed support and generated standing waves 33. What is the period, in seconds, that corresponds to each of the following frequencies: (a) 10 Hz, (b) 0.2 Hz, (c) 60 Hz? Period: T = 1/f. (a) 1/10 = 0.1 seconds. (b) 1/0.2 = 5 seconds. (c) 1/60 = 0.0167 seconds 41. An astronaut on the Moon attaches a small brass ball to a 1.00-m length of string and makes a simple pendulum. She times 15 complete swings in 75 seconds. From this measurement she calculates the acceleration due to gravity on the Moon. What is her result? T = 2π√(L/g) T = 75 seconds / 15 swings = 5 seconds per swing T = 2π√(1.00 m / g)

g = (2π/5 s)^2 / (1.00 m) ≈ 1.6 m/s²