Materials… What happens when?

Explain Why..

Degradation …

Chemical Reactions What is a chemical reaction? What are the signs of a chemical reaction?

Chemical Reactions What is a chemical reaction? A reaction that modifies the nature of a substance (how it is made) and, therefore, changes the properties of the substance

Chemical Review Signs of Chemical Reaction Gas formation Release or absorption of energy (light or heat) Precipitation Color change

Chemical Reactions 2. Types of chemical changes A) Synthesis vs. Decomposition B) Photosynthesis vs. Cellular Respiration C) Oxidation D) Combustion

Chemical Reactions 2. Types of chemical changes A) Synthesis vs. Decomposition Synthesis When 2 or more molecules or elements become one molecule They Combine together Decomposition When 1 molecules is broken down into 2 or more molecules or elements They break apart

Chemical Review 2. Types of chemical changes A) Synthesis vs. Decomposition Synthesis Decomposition

What type of reaction are these? 2 H2(g) + O2(g) → 2 H2O(g) 2 CO(g) + O2(g) → 2CO2(g) 2 NH3(g) →3 H2(g) + N2(g) 4 Al(s) + 3 O2(g) → 2 Al2O3(s) 8 FeS→8 Fe + S8  2 K(s) + Cl2(g) → 2 KCl(s)

Chemical Review 2. Types of chemical changes B) Photosynthesis vs. Cellular Respiration Cellular Respiration What we do Takes in Oxygen Photosynthesis Plants (during the day) Takes in Carbon dioxide

Chemical Reactions 2. Types of chemical changes C) Oxidation Chemical reaction that requires oxygen as a reactant. E.g. corrosion (a.k.a. rust)

Chemical Review 2. Types of chemical changes C) Oxidation Requires Oxygen 2 Mg + O2 ----> 2 MgO E.g. corrosion

Chemical Review with the Particle model 2. Types of chemical changes C) Oxidation Requires Oxygen 2 Mg + O2 ----> 2 MgO + ----> E.g. corrosion

Chemical Reactions 2. Types of chemical changes D) Combustion Chemical reaction that requires oxygen (or oxidizing agent) as a reactant and releases energy.

Chemical Review 2. Types of chemical changes D) Combustion Requires Oxygen as a product Gives off energy CH4 + 2O2 = CO2 + 2 H2O + energy

Combustion side note: Types of combustion: Slow Rapid Spontaneous Requires outside energy input gives off heat and light that is observable Spontaneous

Fuel Oxidation Ignition Agent Temperature Combustion Triumvirate (Fire Triangle) Fuel Oxidation Agent Ignition Temperature

What kind of reaction? CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g)+ energy 2 Fe(s) + O2(g)   2 FeO(s)

Constraints Constraints are Constraints describe The different types of stress the material undergoes Constraints describe the effect of external forces on a material E.g. weight of a building ** Dead load: weight of the bridge itself ** Live load: weight added on the bridge

Types of constraints Compression: When a material is subjected to forces that tend to crush it Hi

Tension When a material is subjected to forces that tend to stretch it That was close

Torsion When a material is subjected to forces that tend to twist it Do you mind?

Deflection When a material is subject to forces that tend to bend it

Shearing When a material is subjected to forces that tend to cut it

Types of material deformation Elastic: When the constraint leads to a temporary change in the shape or dimensions of the material. When the constraint is removed, the material returns to its original form Plastic: The constraint leads to a permanent change in the shape or dimensions of the material. Even when the constraint is removed, the material remains deformed Fracture: The constraint is so intense that it breaks the material