Chemical Reactions Dr. Ron Rusay Spring 2004 © Copyright 2004 R.J. Rusay

General Chemical Reactions  Any chemical reaction can be described as a molecular or atomic change. It produces one or more observable changes.  e.g. color change, gas bubbles, heat, etc.  Reactions are generally described as Reactant(s) --> Product(s)  The reaction is written as a chemical equation with chemical formulas:  2 Na + Cl 2 --> 2 NaCl The atoms that react MUST equal the atoms produced: 2Na, 2Cl = 2Na, 2Cl © Copyright R.J. Rusay

Chemical Reactions & Equations  Chemical equations describe the change(s) in Reactant(s) to Product(s) including physical state(s).  Notations: (g), (l), (s), (aq)  Others: arrows for gas and solid heat, reversibility (for equilibrium) © Copyright R.J. Rusay Na (s) + Cl 2(g) --> NaCl (s ) Write a balanced equation for the formation of sodium chloride.

Types of Chemical Reactions  Combination (Synthesis) **  Decomposition  Single Displacement  Double Displacement  Combustion**  Others: Precipitation, Oxidation- Reduction, Neutralization** © Copyright R.J. Rusay

Chemical Reactions  Combination (Synthesis)  A + B -----> C  Example: © Copyright R.J. Rusay H 2 (g) + O 2 (g) -----> H 2 O (g) Balancing (Conservation of Atoms): H 2 (g) + O 2 (g) -----> H 2 O (g)

Chemical Reactions  Decomposition  A ----> B + C  NI 3 (s) ---> N 2 (g) + I 2 (s)

Decomposition  Another example: Mercury (II) oxide (s) + heat -----> Mercury (II) oxide (s) + heat -----> mercury (s) + oxygen (g) Balanced equation: ? Balanced equation: ? © Copyright R.J. Rusay

Chemical Reactions � Single Displacement � AB + C ----> CB + A � Example: © Copyright R.J. Rusay � (Reaction type is also Oxidation / Reduction) AgNO 3 (aq) + Cu (s) ----> ? Products? AgNO 3 (aq) + Cu (s) ----> ? Products? AgNO 3 (aq) + Cu (s) ----> Cu(NO 3 ) 2 (aq) + Ag (s) AgNO 3 (aq) + Cu (s) ----> Cu(NO 3 ) 2 (aq) + Ag (s) Balanced Equation: ? Balanced Equation: ?

Chemical Reactions  Double Displacement  AB + CD ----> AD + CB  Example: © Copyright R.J. Rusay � (Reaction type is also Precipitation) A solution of silver nitrate reacts with a solution of sodium iodide to produce aqueous sodium nitrate and a precipitate of silver iodide. A solution of silver nitrate reacts with a solution of sodium iodide to produce aqueous sodium nitrate and a precipitate of silver iodide. Balanced equation: ? Balanced equation: ?

Neutralization Reactions HCl(aq) + NaOH(aq)  ? + ?

Chemical Equations Combustion:Combustion: (Reaction type is also Oxidation / Reduction) C 8 H 18(l) + O 2(g) -----> CO 2(g) + H 2 O (l)  Oxygen reacts with octane to produce carbon dioxide and water.  Reminder: the equation must balance:  C 8 H 18(l) + O 2(g) -----> CO 2(g) + H 2 O (l) © Copyright R.J. Rusay

Exothermic Reactions (Give off Heat, a product in the reaction) Endothermic Reactions (Absorb Heat; heat is a reactant) HEAT + Reactants  Products Reactants  Products + HEAT

Exothermic Reactions Chemistry & a soldier’s warm MRE (Meal Ready to Eat ) Magnesium metal (s) + Water (l)  Mg(OH) 2 (s) + hydrogen (g) + HEAT Write a balanced chemical equation for the reaction. What is hazardous in the reaction?

These devices are very helpful for heating MREs, but can cause environmental problems if not properly discarded. The heaters consist of a plastic bag containing a piece of fiber board and powdered magnesium or magnesium alloys and a few other materials. Powdered magnesium is a reactive solid and therefore a hazardous material. The instructions for use specify that the individual using the heater open the top of the bag, pour water into the bag to a specified level, slide the food into the pouch and fold the top down. When heaters are filled with water, the heating process is initiated. The magnesium and water react and the hazardous characteristics are eliminated. Warnings on the pouch indicate that hydrogen, a flammable gas, will be generated during the heating process and warns the user not to place near an open flame. It further warns the user not to use more than ten while in a vehicle or shelter. Adequate ventilation is required due to the hydrogen gas replacing oxygen. Temperatures will normally reach 200 degrees F and may, with insufficient amount of moisture, reach 250 degrees F, which can cause burns on your skin if in contact. Caution is also given about carrying a heater in your clothing because of burns. As long as the MRE Heater is properly used, there is no environmental problem. When the heater is not activated and is discarded as a waste, it must now be treated as a hazardous waste. Hydrogen gas from several heaters can create a dangerous condition. Mixed with other flammable materials in a landfill, it can produce a fire that would be very difficult to extinguish. For proper management and disposal see Policy Memorandum, USAG-HI-7, Management and Disposal of Flameless Ration Heaters, 7 Mar SAFETY ALERT

These devices are very helpful for heating MREs, but can cause environmental problems if not properly discarded. The heaters consist of a plastic bag containing a piece of fiber board and powdered magnesium or magnesium alloys and a few other materials. Powdered magnesium is a reactive solid and therefore a hazardous material. The instructions for use specify that the individual using the heater open the top of the bag, pour water into the bag to a specified level, slide the food into the pouch and fold the top down. When heaters are filled with water, the heating process is initiated. The magnesium and water react and the hazardous characteristics are eliminated. Warnings on the pouch indicate that hydrogen, a flammable gas, will be generated during the heating process and warns the user not to place near an open flame. It further warns the user not to use more than ten while in a vehicle or shelter. Adequate ventilation is required due to the hydrogen gas replacing oxygen. Temperatures will normally reach 200 degrees F and may, with insufficient amount of moisture, reach 250 degrees F, which can cause burns on your skin if in contact. Caution is also given about carrying a heater in your clothing because of burns. As long as the MRE Heater is properly used, there is no environmental problem. When the heater is not activated and is discarded as a waste, it must now be treated as a hazardous waste. Hydrogen gas from several heaters can create a dangerous condition. Mixed with other flammable materials in a landfill, it can produce a fire that would be very difficult to extinguish. For proper management and disposal see Policy Memorandum, USAG-HI-7, Management and Disposal of Flameless Ration Heaters, 7 Mar Meals, Ready-To-Eat (MRE) Flameless Ration Heater (FRH) (NSN ) IFSO SAFETY ALERT