Work - w, heat - q, and internal energy – u
WORK W: Useful Energy Transfered across the System's Boundaries, capable of producing Macroscopic-Mechanical Motion of a the system's Center-of-Mass.
W = Work done by (or on) one system on another system
ENERGY FLOW
OUT: W > 0 System Does External Work Sys —> Work
INTO: W < 0 Work Done on the System Work —> Sys
HEAT Q: Energy Transfer across the System's Boundaries that cannot produce Macroscopic-Mechanical Motion of the system's Center-of-Mass. Energy Transfer at the Molecular Level .
Q = Microscopic Energy flow into (or out of) the System
ENERGY FLOW
INTO: Q > 0 System Absorbs Heat Heat —> Sys
OUT:Q < 0 System Releases Heat Sys —> Heat
INTERNAL ENERGY U Energy Stored in a System at the Molecular Level. The System's Thermal Energy -the Kinetic Energy of the atoms due to their random motion relative to the Center of Mass plus the binding energy (Potential Energy) that holds the atoms together.
U = Microscopic Energy contained in the System
Enthalpy is a defined thermodynamic potential, designated by the letter "H", that consists of the internal energy of the system (U) plus the product of pressure (P) and volume (V) of the system:[1]
Since enthalpy, H, consists of internal energy, U, plus the product of pressure (P) and the volume (V) of the system, which are all functions of the state of the thermodynamic system, enthalpy is a state function.
The unit of measurement for enthalpy in the International System of Units (SI) is the joule, but other historical, conventional units are still in use, such as the British thermal unit and the calorie.
14) Corrosion of metals and ways of protection against it.
Corrosion is the gradual destruction of materials (usually metals) by chemical reaction with its environment.
In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term degradation is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.
Ways of protection against it.
Some metals are more intrinsically resistant to corrosion than others (for some examples, see galvanic series). There are various ways of protecting metals from corrosion (oxidation) including painting, hot dip galvanizing, and combinations of these.
15) Chemical Properties of metals. Metals are Electropositive Elements Metals are very reactive. Metals tend to loose electrons easily and form positively charged ions; therefore metals are called electropositive elements. Sodium metal forms sodium ions Na+, Mg forms positively charged Magnesium ions Mg2+and aluminium forms aluminium ions Al3+. The electropositive nature allows metals to form compounds with other elements easily.
Reaction of Metals with Oxygen
Metals like sodium (Na) and potassium (K) are some of the most reactive metals. Potassium, sodium, lithium, calcium and magnesium react with oxygen and burn in air.
Metals from aluminium to copper in the activity series of metals, react slowly when heated in air to form the metal oxides. Aluminium is the fastest and copper is the slowest of them.
Sodium metal reacts with the oxygen of the air at room temperature to form sodium oxide. Hence, sodium is stored under kerosene to prevent its reaction with oxygen, moisture and carbon dioxide.