Matter and Energy Chapter Energy

Objective/Warm-Up Students will be able to apply their knowledge of density to a real world problem. How can you use density to determine if something will sink or float in water?

Energy Changes Energy – the capacity to do work All physical and chemical changes involve changes in E. Endothermic – describes a process in which heat is absorbed from the environment

Energy Changes Exothermic – describes a process in which a system releases heat into the environment NaOH + H 2 O Evaporation – the change of a substance from a liquid to a gas

Law of Conservation of Energy Law of Conservation of Energy – in a chem. or phys. change, E is neither created nor destroyed It can be transferred or converted Chemical, mechanical, light, sound, heat, electrical

Energy Kinetic Energy – the E a moving object has b/c of its motion Potential Energy – the E an object has b/c of its position

E Transfer In chemistry, the most common E transfer is in the form of heat Heat – the energy transferred b/t objects that are at different temps. Temperature – a measure of the average kinetic E of the particles in a sample of matter.

Temperature Scales

Equations for Temp Conversions t (°C) = T(K) – K T(K) = t (°C) °C Convert 25 °C to Kelvin T(K) = °C = K Convert 1500 K to °C t (°C) = 1500 – K t (°C) = °C

Specific Heat Capacity Specific Heat Capacity – the amount of E required to raise the temp of 1 gram of a substance by 1 Kelvin under constant T & P Different for each element Measured in J/gK – joule is the SI unit for E Determined experimentally

Objective/Warm-Up Students will be able to calculate change in temperature and specific heat capacity. What do the terms endothermic and exothermic mean? How would you know that a reaction is endothermic or exothermic?

Calculations-Specific Heat Q = m c ΔT Q – heat energy (J) m – mass (g) c – specific heat (J/gK or J/g o C) ΔT – change in temperature = (T final – T initial ) (K or o C)

Calculations Calculate the heat required to increase the temperature of 15 g of aluminum by 10. K. The specific heat of aluminum is J/gK Q = 15g x 0.897J/gK x 10.K Q = J ~ 130 J with sig figs ~ 130 J with sig figs

Calculations How much energy is given off when 25 grams of lead cools by 25 K if the specific heat of lead is J/gK? Q = J ~ 81 J with sig figs ~ 81 J with sig figs

Objective/Warm-Up Students will be able to convert temperatures and calculate heat capacity. Warm-Up: Concept Review worksheet

Mass and Energy Thought to be unrelated E=mc 2 relates mass and energy c is equal to the speed of light of x 10 8 m/s In a nuclear power plant, mass is converted to energy

E = mc 2 How much E is obtained from a 1.00 gram object? E = mc 2 E = 1.00 g x (2.998 x 10 8 m/s) 2 E = gm 2 /s 2 or x J It’s enough to raise a burger to your mouth 90 trillion times

Assignment Do the section review on page 45. Do numbers 1-13.