Thermal Energy

Goal of the class To understand the flow of thermal energy in matter Question of the day: How will the flow of thermal energy affect your hot cocoa? Previous answer: Surface tension is the ‘skin’ on a liquid Previous Question: What is surface tension?

Energy Energy comes in many forms and we can sometimes go between them. For example: Chemical  electrical in batteries Potential  kinetic in a swinging pendulum Electrical  sound in a stereo Energy is the ability to do work. Ask about the units of energy

Energy Every chemical or physical change in matter includes a change in energy. Energy must be used the bend a paperclip or energy is given off when you cook you food.

Temperature The motion of particles is related to how much energy they have. The more energy, the faster they move. Temperature is the measure of the average energy of random particles in matter. Ask about 90oC steam when making a cup of tea. Ask about evaporation / how laundry dries How hot tea has more energy than cold tea.

Temperature Scales In everyday life we use the temperature scale called Celsius (°C). It is calibrated using water 0°C is when water freezes 100°C is when water boils In science we use the Kelvin scale(K) – SI unit 0K = -273 °C At 0K there is no motion (called absolute zero) Show that there is no degree sign for Kelvin. Mention Fahrenheit too Same increments Nerdy joke Ask about 0 degree half temperature

Thermal Equilibrium When you put your floor heater on in winter what happens to the heat energy? The reason is because the thermal energy always flows for the hot object to the cold object. Equilibrium means balance. Equivalent volumes example.

Cold? There is no such thing in science as ‘cold’ We can’t measure how ‘cold’ something is. Something that’s cold simply has low thermal energy. Same as how there is no such thing as dark / black.

Energy Flow Direction Sometimes matter absorbs heat and sometime it gives off heat. Placing your cold hands by a warm fire (absorbs) Leaving your hot cocoa on the table (gives out) Endothermic – when heat is taken in. Exothermic – when heat is given off.

Questions How can you tell if a glass of water has more thermal energy than another glass of water? How can you slow down the flow of thermal energy from hot objects to cooler objects? Is ice melting an exothermic or endothermic process?

Vocabulary Kelvin – The SI unit of temperature Equilibrium – Being in balance (no net flow) Exothermic – Heat energy is given off Endothermic – Heat energy is absorbed What does that tell you about water? It’s not an element.

Homework Please complete Chemical Building Blocks workbook pages 16 (finish last 4 questions) and 20-22