Energy Transformations

Energy Changes The study of energy often involves a series of changes. A closed system is one which no energy from the outside gets in or out. In a closed system, the total amount of energy does not change. The total amount of energy given off by an object (energy source) = the total amount of energy absorbed by another object (energy sink)

All energy is conserved 1st Law of Thermodynamics: matter and energy cannot be created or destroyed

Kinetic Energy and Potential Energy All objects in motion have kinetic energy. Energy related to position or state is often thought of as “stored” or potential energy. The movement of matter toward or away from the Earth’s center results in energy tranformations between kinetic and potential energy.

Heat and temperature are often thought to be the same – not so! All particles of matter (atoms, molecules) are in constant random motion. All particles of matter have some kinetic energy. Temperature is a measure of the average kinetic energy of the particles of a sample of matter. What is Temperature?

Temperature Scales “Hot” and “cold” are relative terms, and not useful for describing temperature. Thermometers have several possible temperature scales Fahenheit scale is used in the US Celsius is used in the rest of the world Some branches of physics and chemistry use the Kelvin scale

Temperature Questions Using ESRT

Isotherms on a weather map

Heat Heat is form of energy, not an average. Heat is the total kinetic energy of the particles of a sample of matter. Both of the beakers illustrated below have the same temperature, but the larger one has more heat energy:

Heat Flow Heat always flows from a region of higher energy to a region of lower energy. When two objects are placed in contact with each other, the hotter object will lose kinetic energy to the colder object. The hotter object’s average KE (temperature) decreases, the cooler object’s average KE increases.

Measuring Heat When objects are heated, the heat energy is transformed to kinetic energy – the particles of the object move faster. The average kinetic energy of the particles increase, the temperature increases. Cooling is the opposite..

Measuring Heat A convenient measure of heat energy is the calorie. 1 cal = quantity of heat needed to raise 1 gram of liquid water 1°C A more universal measurement is the Joule (J). 1 calorie = 4.18 J

Specific Heat Different substances heat at different rates – it takes more energy to raise the temperature of some substances than others. The quantity of heat required to raise the temperature of 1 gram of a substance 1°C is called the specific heat of that substance. Every substance has its own specific heat for a particular phase (solid, liquid, gas)

Specific Heat on the ESRT The higher the specific heat, the greater the amount of heat needed to raise the temperature of an equal mass by the same amount.

The same amount of energy is added to equal masses of lead, iron, basalt, and water at room temperature. Assuming no phase change takes place, which substance will have the smallest change in temperature? Lead Iron Basalt Water

Pieces of lead, copper, iron, and granite, each having a mass of 1 kilogram and a temperature of 100°C, were removed from a container containing boiling water and allowed to cool under identical conditions. Which piece most likely cooled to room temperature first? Copper Lead Iron Granite

Heat Energy and Phase Changes: Latent Heat When substances undergo phase changes, additional heat energy will not cause the temperature to rise until the phase change is complete. The added heat is a kind of potential energy, called latent heat.

Latent Heat Loss and Gain Melting, evaporation and sublimation require the addition of latent heat Condensation, freezing and deposition require the loss of latent heat

Water and Latent Heat The latent heat of vaporization is far greater than the latent heat of fusion.

Hurricanes and Latent Heat Hurricanes result in massive transfer of energy from the oceans to the atmosphere and land Kinetic energy  Potential Energy  Kinetic Energy

During which phase change of water is the most energy released into the environment? Water freezing Ice melting Water evaporating Water vapor condensing

Which statement best explains why water in a glass becomes colder when ice cubes are added? The water changes into ice. Heat flows from the water into the ice cubes. Water is less dense than ice. Ice has a higher specific heat than water

Lab 11: Changes in Phase in Water New York State Law requires that you wear safety goggles when heating materials. Fill a beaker to 150 ml 4 ice cubes and 50 ml of cold water. Place the hot plate next to your ring stand. Place the thermometer clamp on the ring stand with the thermometer clamped in. Put the thermometer into the water such that it does not touch any surface of the beaker. Turn on your hot plate and adjust it to a medium level (around 4). The energy source must remain constant throughout the procedure.

Place the beaker on the hot plate Place the beaker on the hot plate. Stir gently with a stirring rod throughout the procedure. Record the temperature every 30 seconds, continuing for at least 10 minutes after the water reaches a full, rolling boil. Record the time in your data when: the ice begins to melt when the ice is entirely melted when water begins to boil Graph your data placing time on the X axis.