Thermal Energy, Heat, and Temperature How are they related? How are they different?

Temperature All matter is made up of tiny particles—atoms and molecules Particles always in constant motion Temperature is the measure of these moving particles, the average kinetic energy of these particles in matter The faster the particles move the warmer the object

Question 1: Which molecules are moving faster due to temperature? Why? Since the hot coffee has a higher temperature the kinetic energy will be faster and therefore the molecules will be moving faster. 100ºC 50ºC

Thermal Energy Total energy of particles in a material, both kinetic and potential *Refresher:* –Kinetic Energy is… –Potential Energy is… Thermal energy increases as the kinetic energy increases Energy in the form of motion Stored energy due to position

Thermal energy depends on: –Mass –Temperature Thermal energy increases as temperature increases and decreases as temperature decreases More mass an object has at same temperature, greater the thermal energy Question 2: Which one has more thermal energy? Why? 50ºC The bathtub has more thermal energy. Even though the temperatures are the same the bathtub has a much bigger mass and therefore has more thermal energy

Heat Thermal energy that flows from higher temperatures to lower temperatures Measured in joules (J), like work and energy Question 3: Does the ice make the drink cold or the drink make the ice warm? Why? The drink makes the ice warm. Heat always flows from warmer to cooler temperatures, therefore the drink would be transferring its heat energy to the ice cubes warming them up and melting them.

Specific Heat (C p ) Amount of energy it takes to raise the temperature of one kg of material one degree Celsius Different materials need different amounts of heat to have similar changes in temperature Specific heat is measured in J/(kg K) or J/(kg °C)

Heat Transfer Which sample will take longer to heat to 100°C? 50 g Al50 g Cu Al - It has a higher specific heat. Al will also take longer to cool down.

Question 4: Which will be warmer the beach or the ocean? Why? The beach will be warmer because it has a lower specific heat (664 J/kg K) and therefore takes less thermal energy to heat up than water which has a much higher specific heat (4184 J/kg K).

Calculating Specific Heat Used to calculate changes in thermal energy since it can not be directly measured Q= m x T x C p –Q is the change in thermal energy –m is mass – T is change in temperature (T final – T initial ) –C p is specific heat If T is positive, temperature has increased and heat is gained If T is negative, temperature has decreased and heat is lost

Calculations You have a 25 g iron horse shoe that went from 25°C to 50°C. The Specific heat of iron is 450 J/kg/K, what is the change in thermal energy of the horse shoe? What do I know?... What do I need to find?... Equation is… Q= m x T x C p So… Now you try… A 45 kg brass sculpture gains 203,000J of thermal energy as its temperature increases from 28°C to 40°C. What is the specific heat of brass? m= 25g =.025 kg Change in Temperature= (50°C - 25°C) Cp= 450 J/kg K Change in thermal energy, Q Q=.025kg(25°C)(450 J/kg K) Q= J