• Energy: the capacity to do work or to produce heat

○ J = SI unit for energy

■ kJ = 10^3 J

• Work: force acting over a distance

○ W =

•  Potential Energy: due to position or composition (stored energy) → can be converted to work

○ Ex: water behind a dam, saturated fat (energy stored in bonds), attractive and repulsive forces

Kinetic Energy: energy due to motion of the object

M = mass of object in kg; v = velocity of object in m/sec

• State function: value that depends on the state of the substance, not how that state was reached

○ Ex: internal energy, pressure, volume, density, enthalpy

■ Note: work and heat are not state functions

System and Surroundings

• System: that on which we focus attention

○ Ex: The solute, solution or gas in a container, reactants and products (the reaction)

• Surroundings: everything else in the universe

○ Ex: Ourselves (ie hands), a thermometer, reaction vessel (beaker), the solvent are part of the surroundings

○ When we measure temp changes during a chemical reaction, we are measuring the surroundings

• Universe = System + Surroundings

Exo and Endothermic

• Heat exchange/temp change accompanies:

○ Heatingor cooling a substance

○ Phase changes

○ Dissolving solutes

○ Chemical reactions

• Exothermic: energy is released by the system (to the surroundings)
• Endothermic: energy is absorbed by the system (from the surroundings)

Exothermic Processes

• Cooling an object
• Exothermic Phase changes: freezing; condensation; deposition
• Some chemical & dissolution reactions (feel hot) → temp (of surroundings) is increasing
• Electron affinity:
• Solute and Solvent Interactions: in exothermic reactions, the solute and solvent particles are more

strongly attracted to each other than they are to themselves

• In an exothermic process, some kind of bond or attractive force is forming!

○ “Free to form”

○ Justify: The energy required to break bonds (positive) is less than the energy released when the bonds are formed (negative) → process is energetically favorable → ΔH⁰ = negative

Endothermic Processes

• Heating an object
• Phase changes:

○ Melting; vaporization; sublimation

• Some chemical and dissolution reactions (feels cold) → temp (of surroundings) is decreasing
• Solute and Solvent Interactions: in endothermic reactions, the solute and solvent particles are more  are breaking the forces of attraction between sodium and its valence  electron strongly attracted to themselves (stronger interactions) than they are to each other.
• In an endothermic process, some kind of bond or attractive force is breaking

○ “Takes (energy) to break”

○ Justify: The energy required to break bonds is more than the energy released when the bonds are formed → ΔH⁰ = positive

■ If temp graph is shown: because temp decreased, energy flows into the process