Thermodynamics Notes – Day 1

Heat, energy and temperature in our lives… Deciding what you are going to wear during the day and at night when you go to bed. How many covers you will put on you at night, in order to maintain the right temperature. Most homes, schools & work have heating and cooling systems which control the temperature so that the temperature is just right. Some people install fans or use portable fans in homes to keep comfortable in the summer. Also, people buy portable heaters and generators to keep warm in the winter. Most of us have cars that are equipped with heating and air conditioning systems; some may even have a meter that registers the indoor and outdoor temperatures. Many of us watch and listen to weather reports so that you can make a decision on what to wear. You probably remember mom or dad sticking a thermometer under your tongue (or elsewhere) to get your body temperature to see if you had a fever.

Our bodies are very sensitive to hot and cold… We learn very early in life that we shouldn’t touch a hot pan on the stove or a hot light bulb in a lamp. We also learn to be careful about tasting hot foods or drinks. We all know the experience of sweating, our bodies built-in mechanism of cooling us down when temperatures begin to rise.

Temperature and Heat The temperature of a hot cup of coffee left sitting on the table will fall until it reaches thermal equilibrium with the air temperature in the room. When a soda can is taken out of the refrigerator and left on the kitchen table, its temperature will rise – rapidly at first but then more slowly – until the temperature of the soda equals that of the air in the room. At this point, the soda and the air temperature in the room are in thermal equilibrium. The change in temperature is due to the transfer of energy between the object and the environment.

Thermal Equilibrium When the flow of energy from one body into another equals the flow of energy in the reverse directions, the objects are in thermal equilibrium. They both have the same temperature. Thermal energy always travels spontaneously from hot to cold.

Remember this??? Thermal energy moves in a predictable pattern from warmer to cooler until all the substances attain the same temperature such as an ice cube melting. You learned this in the 6 th grade!!!

Temperature and Heat Thermal energy: the total potential and kinetic energy associated with the random motion and arrangement of the particles of a material. Heat, Q, is thermal energy that is simply transferred from one body to another. – Heat is thermal energy in motion. – Heat is used when the transfer of thermal energy from one body to another body at a different temperature is involved.

Temperature Temperature is a measure of the average kinetic energy of the molecules which make up a substance. -The temperature of a substance will increase/decrease if the average kinetic energy of its particles is increased/ decreases. -The SI unit of temperature is the kelvin (K). One kelvin equals one degree Celsius. Zero degrees Celsius equals K.

Temperature Central concept of thermodynamics is temperature. – Our “temperature sense” is often unreliable. – On a cold winter day, an iron railing seems much colder to the touch than a wooden fence post, even though both are at the same temperature. – This error in perception results because the iron removes energy from our fingers more quickly than the wood does.

Specific heat Every substance gains or loses heat based on it’s identity. This physical property of the substance is called the specific heat capacity of the object. The specific heat capacity, (c), of a solid or liquid is defined as the heat required to raise a unit of mass of the substance by one degree of temperature.

Google It! What is the specific heat of…… – Water? – Sand?

Specific Heat is the measure of how much thermal energy is required to change the temperature of a substance. Heat = (mass)x specific x change Energyheat in temp OR Q = m c  T

Heat Change To determine the amount of thermal energy gained or lost by a mass: Heat energy is gained if Q is positive. Heat energy is lost if Q is negative.

Example 1. A 4.0 kg sample of glass heated from 1 o C to 41 o C, and was found to have absorbed 32 J of energy. What is the specific heat of the glass? Q = m C ΔT

Example 1. A 4.0 kg sample of glass heated from 1 o C to 41 o C, and was found to have absorbed 32 J of energy. What is the specific heat of the glass? Q = m C ΔT ΔT = 41 o C – 1 o C = 40 o C 32 J = (4.0 kg) C (40 o C) 32 J = (160 kg o C) C C = 0.2 J/kg o C You will need to know units for your test!!

Example 2 To what temperature will a 20.0 g piece of glass raise if it absorbs 6000 joules of heat and its heat capacity is 0.50 J/gºC? The initial temperature of the glass is 20.0ºC.

Example 3 What is the Specific heat capacity of silver metal if g of the metal absorbs 400 joules of heat and the temperature rises 30.0ºC?