Chapter 5: Heat (Molecules In Motion)

Heat can flow in three different ways: conduction, convection, and radiation. Conduction is the transfer of heat through direct contact between objects or substances. Convection is the transfer of heat through the movement of fluids, such as air or water. Radiation is the transfer of heat through electromagnetic waves, such as infrared radiation. These three processes play a crucial role in the transfer of heat from one object to another.

Conduction is the transfer of heat by direct contact between two objects. It occurs when there is a temperature difference between the objects, causing the heat to flow from the hotter object to the cooler one. This transfer of heat happens through the collision of molecules in the objects, where the faster-moving molecules transfer their energy to the slower-moving ones. Conduction is commonly observed in solids, where the molecules are closely packed and can easily transfer heat through direct contact.

Entropy is the correct answer because in thermodynamics, it refers to the measure of the amount of disorder or randomness in a system. It is a fundamental concept that helps describe the direction of spontaneous processes and the availability of energy in a system. Entropy increases in isolated systems over time, leading to a higher level of disorder.

Kelvin is the correct answer because it is a temperature scale that measures absolute temperature. Unlike Celsius and Fahrenheit, which are relative scales, Kelvin starts at absolute zero, the lowest possible temperature. It is commonly used in scientific and engineering applications where precise temperature measurements are required. The Kelvin scale is based on the concept of molecular motion, where zero Kelvin represents the complete absence of molecular motion.

Entropy is the correct answer because it refers to the amount of disorder or randomness in a system. In thermodynamics, entropy is a measure of the unavailability of a system's energy to do work. It quantifies the level of chaos or randomness in a system. The higher the entropy, the greater the disorder in the system. In other words, entropy is a measure of the system's tendency to move towards a state of equilibrium or maximum disorder.

A solute is a substance that dissolves in a liquid. This means that when the solute is added to the liquid, it disperses evenly throughout the liquid, forming a homogeneous mixture. The solute particles become surrounded by the solvent particles, which allows for the dissolution process to occur. Examples of solutes include salt dissolving in water or sugar dissolving in tea.

Radiation is the transfer of heat by electromagnetic waves. Unlike conduction and convection, which require a medium such as a solid or a fluid, radiation can occur through empty space. This process involves the emission of electromagnetic waves, such as infrared radiation, by a hot object and the absorption of these waves by a cooler object. This transfer of energy through electromagnetic waves is how heat from the Sun reaches the Earth, and it is also how heat is emitted by objects like heaters or fire.

Heat transfer through fluids occurs through convection. Convection is the process of heat transfer in which heat is transferred through the movement of fluids, such as liquids or gases. This transfer of heat occurs due to the movement of the particles within the fluid, which carry the heat energy from one location to another. Convection is commonly observed in everyday life, such as the rising of hot air or the circulation of water in a boiling pot.

Sir Humphry Davy invented the Miner's safety lamp. He developed this lamp in the early 19th century to prevent explosions in coal mines caused by the ignition of flammable gases. The lamp had a wire gauze surrounding the flame, which allowed light to pass through but prevented the flame from igniting the surrounding gas. This invention significantly improved the safety conditions for miners, as it reduced the risk of deadly explosions in the mines.

Condensation is the process by which a gas returns to its liquid state. When a gas cools down, its particles slow down and come closer together, causing them to form liquid droplets. This change of state is known as condensation.

When the temperature of a liquid increases, the kinetic energy of its molecules also increases. This leads to an increase in the average speed of the molecules, causing more molecules to have enough energy to escape from the liquid's surface and enter the gas phase. As a result, the rate of evaporation increases.

Heat of vaporization is the correct answer because it refers to the quantity of heat required to change a given amount of liquid, already at its boiling point, into a gas without raising its temperature. This process involves the conversion of the liquid's molecules into a gaseous state, and it requires a specific amount of energy, known as the heat of vaporization. This term is commonly used in thermodynamics and is an important concept in understanding phase changes and the behavior of substances when transitioning between liquid and gas states.

Volatile is the correct answer because it describes liquids that evaporate quickly. Volatile substances have low boiling points and high vapor pressures, allowing them to easily transition from a liquid to a gas state. This rapid evaporation is due to the weak intermolecular forces present in volatile liquids.

BTU stands for British Thermal Unit. It is a unit of measurement commonly used in the energy industry to measure the amount of heat energy required to raise the temperature of one pound of water by one degree Fahrenheit. This unit is widely used in heating and cooling systems to determine the heating or cooling capacity of appliances such as air conditioners, furnaces, and heaters.

The correct answer is "fusion" or "Fusion". The latent heat required to change a given mass of a solid into a liquid without changing its temperature is called heat of fusion. This term refers to the energy needed to overcome the attractive forces between the particles in a solid and convert it into a liquid state. It is a specific type of phase transition where a substance changes from a solid to a liquid.

The first law of thermodynamics states that the total of the mass and energy in a system is constant. This means that energy cannot be created or destroyed, but it can be converted from one form to another. The law emphasizes the conservation of energy within a closed system, where the total amount of energy remains constant. Therefore, the correct answer is "Constant."

The process in which a solid substance changes into its liquid form is called melting.

When temperatures are extremely high, molecules are broken apart and electrons are knocked loose from their atoms, resulting in a state of matter called plasma. Plasma is often referred to as the fourth state of matter and is characterized by its ionized state, where positively charged ions and free electrons coexist. It is commonly found in stars, lightning, and certain types of flames.

The temperature at which a liquid changes into a solid is referred to as its freezing point. This is the specific temperature at which the liquid molecules lose enough energy to form a solid lattice structure. The freezing point is a characteristic property of each substance and can vary depending on factors such as pressure and impurities.

Cold is merely a state of lower thermal energy. When an object or environment is described as cold, it means that it has a lower temperature compared to its surroundings. Coldness is a subjective perception caused by the transfer of heat from the body to the colder object or environment. It is not a form of energy transfer like conduction or radiation, nor is it a physical force like wind. Therefore, the correct answer is cold.

When a gas changes directly into a solid and/or a solid changes directly into a gas, the process is known as sublimation. This occurs when the substance bypasses the liquid phase and transitions directly between the gas and solid states. An example of sublimation is when dry ice (solid carbon dioxide) turns into carbon dioxide gas without melting into a liquid first.

A thermostat is a device that automatically regulates temperature. It is commonly used in heating and cooling systems to maintain a desired temperature by turning on or off the heating or cooling system as needed. Unlike a thermometer, which only measures temperature, a thermostat actively controls it. A barometer measures atmospheric pressure, while an A/C unit is a device used for cooling a space. Therefore, the correct answer is thermostat.

Heat is the transfer of thermal energy from an object of higher temperature to an object of lower temperature. This process occurs naturally and is governed by the laws of thermodynamics. When two objects with different temperatures come into contact, the hotter object will transfer its thermal energy to the cooler object until they reach thermal equilibrium. This transfer of energy is what we perceive as heat. Therefore, the statement "Heat is the transfer of thermal energy from an object of higher temperature to an object of lower temperature" is true.

The Greenhouse Effect is an example of radiation because it involves the transfer of heat through electromagnetic waves. In this process, the Earth absorbs solar radiation and emits infrared radiation, which is trapped by greenhouse gases in the atmosphere. This trapped radiation leads to an increase in temperature, causing global warming. Convection and conduction, on the other hand, involve the transfer of heat through physical contact or movement of particles, which is not the primary mechanism involved in the Greenhouse Effect.

The Second Law of Thermodynamics states that heat and other natural processes in a system tend to go only toward lower total energy and greater disorder. This law is also known as the law of entropy. It explains that in any spontaneous process, the total entropy of a closed system will always increase over time. This means that energy tends to disperse and become less organized, resulting in an increase in disorder or randomness.

The specific heat of a substance refers to the amount of heat energy required to raise the temperature of a given mass of that substance by 1 degree. Therefore, the statement in the question is explaining the concept of specific heat. The correct answer, "Specific Heat" or "specific heat," aligns with this explanation.

The equation for work is represented by the letter "W" and is equal to the product of force "F" and displacement "D". The equation is case sensitive, meaning both uppercase and lowercase letters are valid representations. Therefore, the correct answer is W=FD, W=fd, w=FD, w=fd.

The rate of evaporation is determined by two factors. The first factor is the temperature, as higher temperatures increase the kinetic energy of the liquid particles, causing them to move faster and evaporate more quickly. The second factor is the surface area of the liquid, as a larger surface area provides more exposed particles that can escape into the air.

The factors that affect thermal energy are the temperature of an object, the mass of the object, and the specific heat of the substance. Temperature refers to the average kinetic energy of the particles in an object, which determines the amount of thermal energy present. Mass is the amount of matter in an object, and it affects the total thermal energy because more mass requires more energy to heat up. Specific heat is the amount of energy required to raise the temperature of a substance by a certain amount, and it determines how efficiently a substance can absorb and retain thermal energy.