CHM 2045C

Chapter 6:†† Principles of Reactivity: Energy & Chemical Reactions

Key Terms

 

 

0.†††††††† Calorimeter: a device used for measuring the heats of chemical reactions.

 

1.†††††††† Calorimetry: the experimental determination of the heats of chemical reactions.

 

2.†††††††† Chemical potential energy: the potential energy associated with chemical bonding.

 

3.†††††††† Cold: the absence of heat

 

4.†††††††† Electrical energy: the energy of electrons moving through a conductor.

 

5.†††††††† Electrostatic energy: the potential energy that is associated with the separation of two charges.

 

6.†††††††† Endothermic process: a process in which heat is transferred from the surroundings to the system.

 

7.†††††††† Energy: the capacity to do work.

 

8.†††††††† Enthalpy: the heat content of a substance at consistent pressure.We abbreviate enthalpy by the letter H and changes in enthalpy by ΔH.

 

9.†††††††† Exothermic process: a process in which heat is transferred from the system to the surroundings.

 

10.†††††† First Law of Thermodynamics: another name for the law of conservation of energy.

 

11.†††††† Gravitational energy: the potential energy that results from the attraction of any two masses.

 

12.†††††† Heat: the flow of energy from an object at a higher temperature to an object of lower temperature

 

13.†††††† Heat of fusion, ΔH fus: the heat required to convert a solid at the melting point to a liquid,

 

14.†††††† Heat of vaporization, ΔH vap: the heat required to convert a liquid at its boiling point to a gas.

 

15.†††††† Hessís law: if a reaction is the sum of two or more other reactions, ΔH for the overall process is the sum of the ΔH values of those reactions.

 

16.†††††† Internal energy: for a chemical system, this is the sum of the potential and kinetic energies of the atoms, molecules, or ions in the system.We abbreviate internal energy by the letter E and change in internal energy by ΔE.

 

17.†††††† Kinetic energy: the energy of motion.

 

18.†††††† Law of conservation of energy: energy is neither created nor destroyed in ordinary processes.

 

19.†††††† Mechanical energy: the energy of a moving object at the macroscopic level.

 

20.†††††† Potential energy: energy that results from an objects position; stored energy.

 

21.†††††† Sound (or Sound Energy): a type of energy that results from the compressions and expansions of the spaces between molecules.

 

22.†††††† Specific heat capacity: the quantity of heat required to raise the temperature of 1 gram of a substance by one Kelvin unit or one degree Celsius.

 

23.†††††† Standard molar enthalpy of formation, ΔHof , the enthalpy change for the formation of 1 mole of a compound directly from its component elements in their standard state.

 

24.†††††† Standard state: for an element or compound this is the most stable form of the substance in the physical state that exists at pressure of 1 bar (approximately 1 atmosphere) at a specified temperature.For a solute, the concentration is 1 M.

 

25.†††††† State function: a function whose value is determined only by the state of the system and not by the pathway by which that state was achieved.

 

1.†††††††† Sublimation: the change of state in which a material changes directly from the solid state to the gaseous state without passing through the liquid state.

 

2.†††††††† Surroundings: everything outside the system that can exchange energy with the system.

 

3.†††††††† System: the object, or collection of objects, being studied.

 

4.†††††††† Temperature:†† a property that determines the direction of heat transfer; heat transfers from at a higher temperature to something at a lower temperature.

 

5.†††††††† Thermal energy: heat energy due to the motion of atoms, molecules, and ions.

 

6.†††††††† Thermal equilibrium: the condition at which two objects are at the same temperature.

 

7.†††††††† Thermodynamics: the science of heat and work.

 

8.†††††††† Work: work is done when a force, F,is applied through a distance, d.

††††††††††† Mathematically, w = F x d.

 

Forms of Energy:

 

a) Mechanical Energy of Motion

Energy exhibited by objects in motion.

Example: any moving object.

 

b) Thermal Energy

Unorganized energy of motion exhibited by vibrations of atoms and

molecules.

Example: rub hands together.

 

c) Sound Energy

Organized energy of motion exhibited by vibrations of atoms and

molecules.

Example: any sound.

 

d) Electrical Energy

Energy resulting from the forces between charged particles.

Example: Electrical energy from a hand-cranked generator lights a

bulb.

 

e) Magnetic Energy

Energy resulting from the forces between magnets, causing the

magnets to attract or repel. Example: one magnet floats above

another magnet.

 

f) Radiant Energy

Energy resulting from the vibrations of charges, such as radio

waves, microwaves, light rays, and X-rays.

Example: radiant energy

from a floodlight shining on a solar cell powers the free play radio.

 

g) Gravitational Potential Energy

Energy stored in raised objects, which have the potential to fall.

Examples: water wheel or any raised object.

 

h) Strain Potential Energy

Energy stored in stretched or compressed objects, such as springs.

Examples: music box and wind-up toys.

 

i) Electrical Potential Energy

Energy stored in the separation of static (not moving) electric

charges.

Example: capacitor

 

j) Chemical Potential Energy

Energy available in the chemical bonds between atoms or molecules.

Example: battery

 

k) Nuclear Energy

Energy available in the nucleus of atoms that can decay.

Examples: smoke detector, the Sun