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Thermal Energy & Society. In this chapter we will explore ; The physical concepts of temperature , thermal energy , and heat . Explain the temperature changes involved in changes of state , and mathematically determine the energy involved.
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Thermal Energy & Society In this chapter we will explore; • The physical concepts of temperature, thermal energy, and heat. • Explain the temperature changes involved in changes of state, and mathematically determine the energy involved. • Problem solving involving the quantity of heat and situations involving heat exchange. • Describe the impact of heating and cooling systems on society and the environment.
6.1 Warmth & Coldness You dip your toe into a swimming pool to get a physical sense of how warm or cold the water is. While touch helps us sense large differences in warmth and coldness, small differences can go unnoticed. What is the difference between warm and cold water? Why is warm water warm, and cold water cold? How can we accurately measure the warmth and coldness of substances?
6.1 Warmth & Coldness The kinetic molecular theory is based on the idea that matter is composed of atoms and molecules that attract each other and have kinetic energy. It is the kinetic energy (EK) that causes the particles to be in a constant state of motion. An increase in the motion of the particles of a substance makes the substance feel warmer; a decrease in the motion makes the substance feel colder.
6.1 Warmth & Coldness In a solid, particles are held in fixed positions by the forces of attraction between them, and vibrate because of the kinetic energy they posses. In a liquid, particles have more EKthan a solid, causing them to vibrate more rapidly and move from place to place; the ability to flow. In a gas, particles have more EKthan a liquid, allowing them to move much farther and more rapidly. Particles can move freely past each other.
6.1 Thermal Energy The total amount of kinetic and potential energy possessed by the atoms or molecules of a substance is called thermal energy (ETH). The kinetic energy is associated with the motion of the particles; the potential energy with the force of attraction between these particles. The amount of thermal energy within a substance determines how fast its particles move; how hot or cold the substance is. When an object or substance absorbs thermal energy, it warms up; when it releases thermal energy, it cools down. Thermal energy can be transferred from a warmer to a colder substance, but not from a colder to a warmer substance.
6.1 Temperature How can we measure the amount of thermal energy a substance has? There is no way to measure the total amount of thermal energy within a substance, because it is impossible to measure the kinetic and potential energy of every particle. Instead, scientists measure the average kinetic energy of the particles in a substance to give an indication of how hot or cold a substance is; this is the temperature of a substance. Temperature is often measured using a mercury or an alcohol thermometer.
6.1 Temperature Scales Celsius Scale → Based on the temperature of the boiling and freezing points of water. Pure water freezes at 0 °C and boils at 100 °C. Fahrenheit Scale → Based on the temperature of the boiling and freezing points of brine (salt-water) solution. Pure water freezes at 32 °F and boils at 212 °F. Kelvin Scale → Based on absolute zero, the point where there is no motion in the particles of a substance. It occurs at 0 K; -273 K. TC = TK – 273 Kelvin to Celsius; TK = TC + 273 Celsius to Kelvin SP # 1,2 p.273
6.1 Temperature and Physical State Substances increase in temperature when they absorb thermal energy and decrease in temperature when they release thermal energy. Eventually the substance will change from one physical state to another. The temperature at which a solid substance melts into a liquid is the melting point; conversely, the temperature at which a liquid freezes into a solid is the freezing point. For most substances the melting point is the same as the freezing point. The temperature at which a liquid substance changes into a gas is called the boiling point; conversely, the temperature at which a gas changes into a liquid is the condensation point. For most substances the boiling point is the same as the condensation point.
6.1 Homework • Practice # 1, 2 p.273 • Questions # 1-4, 6, 7 p.274
