Matter in Motion The molecules that make up matter are in constant motion. These molecules have kinetic energy.

Why do objects feel hot or cold? Temperature is the average kinetic energy of atoms or molecules. The faster the molecules are moving, the more kinetic energy, and the higher the temperature.

Thermal Energy Thermal Energy is the sum of kinetic and potential energy of all the molecules in an object. Example: Cold butter softens when has been sitting out at room temperature. –Which has a higher temp—air or butter? –Which has a higher kinetic energy? –How does the butter soften? Air

Thermal Energy vs. Temperature When temperature increases, the average kinetic energy increases. When kinetic energy increases, the thermal energy increases, as well.

Thermal Energy and Mass Suppose you have a glass and a beaker of water at the same temperature. The beaker contains twice as much water as the glass, so the average kinetic energy is the same in both containers However, there are twice as many water molecules in the beaker as there are in the glass, so the total kinetic energy is greater in the beaker. As a result, even though at the same temperature, the beaker water has twice as much thermal energy as the water in the glass.

Heat Heat is thermal energy that flows from something at a higher temperature to something at a lower temperature. Heat is a form of energy so measured in Joules (J). Heat always flows from warmer to colder materials.

Specific Heat As a substance absorbs heat, its temperature change depends on the nature of the substance, as well as the amount of heat added. The amount of heat that is needed to raise the temperature of 1 kg of some material by 1°C or 1 K is called the specific heat of a substance.

Water as a Coolant Water has a high specific heat. This is because water molecules have a strong bond between each other. Because water can absorb heat without a large change in temperature, it is useful as a coolant. A coolant is a substance that is used to absorb heat.

Calculating Thermal Energy The change in thermal energy is related to the mass of the object, its specific heat, and its change in temperature in this way. Formula: Q = m x ΔT x C –Q = thermal energy –m = mass –ΔT = (T final – T initial ) –C = specific heat

Thermal Energy Examples How much energy must be transferred to 420 kg of water in a bathtub in order to raise the water’s temperature from 25°C to 37°C? (specific heat of water = 4186 J/kg · K) How much energy is needed to decrease the temperature of kg of iron from 403 K to 283 K? (specific heat of iron = 449 J/kg · K)

Energy and Chemical Change Endothermic Reactions = energy absorbed –Products have more energy than reactants. –Takes energy away from surroundings & use to form the bonds in the products. –Temperature of system decreases.

Energy and Chemical Change Exothermic reactions = energy released –Products have less energy than reactants. –Extra energy holding the bonds of the reactants together is released as heat because it is not needed to make bonds of the products. –Temperature of system increases.