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Thermodynamics of Chemistry
Types of Energy Temperature vs Thermal Energy Measuring Heat Showing Enthalpy Calculating Enthalpy Using heats of formation Using Hess’s Law Using Bond energies Entropy Gibbs free energy Extra Practice
i.e. specifically related to chem
System, Surroundings and Temperature Fun fact: a 1.2° increase in temperature above the norm in the ocean off the west coast of Africa is where the energy required to generate a hurricane comes from.
12 4 Laws of Thermodynamics
- Zeroth Law: If two things are both in balance with a third thing (in terms of temperature), they must also be in balance with each other. For example, if A is in thermal balance with B, and B is in thermal balance with C, then A and C must also be in thermal balance.
- First Law: Energy can't be created or destroyed. It can only change from one form to another (like heat, work, or matter). So, if energy is added or taken out of a system, the internal energy of that system will change accordingly.
- Second Law: In any natural process, the total "disorder" (called entropy) in a system will either stay the same or increase. It’s also why heat naturally flows from hot objects to cold ones—not the other way around.
System vs. Surroundings
- (^) The system is where the “event” occurs,
- (^) The surroundings are everything in the vicinity that doesn’t participate in the event.
- (^) It is important to remember that thermal energy only moves from the hot object to the cold object.
Measuring Thermal Energy Flow
- (^) The flow of Heat is the transfer of thermal energy from a
body at high temperature to a body at a lower
temperature.
- (^) Thermal energy is the amount of energy filling an object (proportional to mass) and the sum of all the particle K.E..
- (^) If a small pond and a large lake are at the same temperature, the lake is holding more energy (because it has more particles than the pond and it is made of the same material).
Converting T to E
- q = mc p T Every material has its own specific heat; specific heat is the amount of energy required to raise one gram of that material by one Celsius or Kelvin degree.
Phase change energy is used to break the intermolecular
forces of attraction between
molecules (not to increase KE of molecules themselves) nH = phase change energy No T during phase changes
q=mc p ΔT is used to calculate the amount of thermal energy that has entered or left an object while it is in a particular phase.
3.216 kJ 13.364 kJ 16.763 kJ 90.354 kJ
- 3.216 kJ 126.913 kJ 127 kJ
Heat Lost = Heat Gained
2.00g Benzoic Acid Releases 52.76 kJ q = -q
q = - q
q = CT
1 st Law of Thermodynamics Energy is neither created nor destroyed, the amount of energy in the
universe is constant.
E universe = E system
- E surroundings Restated, the energy of a system is the combination of the amount of heat (q) lost or gained and the amount of work (w) done by or on the system. E system = q + w Energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed
Chemical energy
- (^) Energy stored in covalent bonds (electron
configurations that hold atoms together).
- (^) Energy is required/absorbed to break bonds.
- (^) Energy is released when bonds are formed. Using copper and zinc nails and the acid from lemons, chemical energy can be converted into electrical energy.
