Chapter 10 Energy THERMODYNAMICS

WHAT IS THERMODYNAMICS? All chemical reactions involve a change in energy between a system and its surroundings. Thermo=Heat Dynamics=change Energy=heat in chemistry Thermodynamics is the study of energy transfers that occur as… Heat is absorded: added to the reaction Heat is evolved: given off as a product of the reaction

MEASURING HEAT TRANSFER Heat is symbolized by the letter q Heat is measured in Joules or kilojoules (kJ) 1000J=1kJ Example: Convert 12,000 Joules to kJ Answer: 12

TEMPERATURE VS. HEAT Temperature: a measure of the average kinetic energy of the particles in a sample matter. Measured in Celsius ( o C), Kelvin (K) Kelvin scale does not have negative numbers In order to convert between celsius and kelvin you just add 273 Example: Convert 25 o C to Kelvin. Answer: 298 K

TEMPERATURE VS. HEAT CONT… Kinetic energy is the energy of motion Temperature measures how fast the average molecule is moving in a sample The faster the molecules, the higher the temperature The slower the molecules, the lower the temperature

ENTHALPY Heat- the total amount of energy, movement Enthalpy (ΔH) is the heat of a reaction- Change in heat of the products from the reactants Heat will either be absorbed or given off

Reactions that require an input of energy (heat) CO 2 (g) +2H 2 O (g)  2O 2 (g) + CH 4 (g) ΔH is positive Reactions that release heat H 2 (g) + Cl 2 (g)  2HCl (g) ΔH is negative ENDOTHERMIC VS EXOTHERMIC exothermicendothermic

PHASE CHANGES Phases: solid, liquid, gas

PHASE CHANGES Δheat of fusion- the energy it takes to go from solid  liquid; it is a positive value, it requires energy -Δheat of fusion- is the reverse. It is the energy required to go from liquid  solid. It is the same amount of energy, but negative and energy is released. Δheat of vaporization-the energy it takes to go from liquid  gas. It is a positive value, it requires energy. -Δheat of vaporization-is the reverse. It is the energy required to go from gas  liquid. It is the same amount of energy but negative, energy released.

SPECIFIC HEAT (PHASE CHANGE PROBLEMS) Formula: q=msΔT q-heat, s-specific heat, m- mass, ΔT-change in temperature in degree Celsius