Heat: Lesson 4 Heat vs. Temperature

What happens to the movement of molecules as they’re heated? /energy-forms-and-changeshttp://phet.colorado.edu/en/simulation /energy-forms-and-changes

What is temperature? Temperature is the average kinetic energy of matter. The more the molecules move the higher the temperature will be. =

Thermal Energy Thermal energy is the total amount of energy in a sample. It involves the temperature and amount of a substance. +

Which sample has more thermal energy? 50 mL at 100 °C 100 mL 100 °C Sample A Sample B =thermal energy

Which one has more thermal energy: A or B? 50 mL at 80 ° C10 mL at 100 ° C 100 mL temp increases from 22 °C to 38 ° C 100 mL temp increases from 22 °C to 29 ° C A B

Law of Conservation of Energy The amount of energy released in a system must be equal to the amount of energy absorbed by the surroundings. System Releases 54 calories Surroundings Absorbs 54 calories

The amount of energy released or absorbed by a process can be quantified by the following equation: q = m x x ΔT q = heat m = mass ΔT = Change in Temperature (T final – T initial ). 1 calorie is the amount of energy that it takes to raise 1 gram of water 1°C.

PRACTICE: A 100 gram sample of water is at 50°C. The water sample cools to 25°C. How many calories did the sample lose to the surroundings? q = m x x ΔT q = ? m = 100g ΔT = (25°C – 50°C) = (–25°C ) q = 100 x x –25°C q = cal PLUG IN AND SOLVE:

PRACTICE: 200 mL of 50°C water is mixed with 75 mL of 90°C water. The final temperature of the water is 60.9°C. How much heat did the 50 °C water gain? q = ______ m = ______ ΔT = (T final – T initial ) = (___ – ___) = ( _____ ) q = m x x ΔT PLUG IN AND SOLVE:

PRACTICE: 200 mL of 50°C water is mixed with 75 mL of 90°C water. The final temperature of the water is 60.9°C. How much heat did the 90°C water lose? q = ______ m = ______ ΔT = (T final – T initial ) = (___ – ___) = ( _____ ) q = m x x ΔT PLUG IN AND SOLVE:

This example proves the Law of Conservation of Energy because the energy gained by the colder water, 2180 calories, is equal to the energy lost by the hot water, 2180 calories. Hot Water Lost 2180 calories Cold Water Gained 2180 calories