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Chemical Reactions

Investigation 1 – Concept Day

 

 

 

 

 

 

 

Chemical Reactions: Investigation 1

Concept Day

SLIDE CHEM-1-1

  • This Investigation is designed to help you understand that there are common features among chemical reactions.

Note: In Investigations 1 through 3 we will study three different reactions. In this Investigation, we will follow the reaction:

NH4OH + HCl → H2O + NH4Cl

Note: This is an exothermic reaction and therefore gives off heat. You will measure the heat released by the reaction in a calorimeter to watch the reaction progress. You will increase the amount of reactants in three Trials and see what effect reactant concentration has on product formation.

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SLIDE CHEM-1-2

  • This slide introduces the important concept of reactants and products.
  • Look at the slide carefully.
  • The reactant molecules are altered by the chemical reaction and reconfigured into the product molecules. This is depicted by the different shapes and colors of the reactant molecules and the product molecules.

Note: It is important for you to understand that the atoms in the reactant molecules rearrange themselves into the product molecules. This will be more apparent on the next slide.

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SLIDE CHEM-1-3

  • This slide presents two chemical reactions that introduce real reactants and products instead of the colored symbols on the previous slide. 
  • You can “read” a chemical equation as a sentence.

Note: The first equation is read, “The reaction between sodium chloride and silver nitrate yields sodium nitrate and silver chloride”.

  • All chemical equations may be read like this.
  • Every atom in the reactants turns up in the products in the exact same amount. Atoms in the reactants and the products MUST be the same; otherwise, matter would be created or destroyed in the chemical reaction! 

Note: The tables below provide a “bookkeeping” strategy for being sure all atoms on both sides (reactants and products) are accounted for. Notice in the second reaction (this is the reaction for photosynthesis) one must take into account the number of molecules of each reactant and product:

AgNO3

PhotoSynth

  • The conservation of atoms in the reactants and products leads to one of the most fundamental principles of physics and chemistry, the Conservation of Matter.

Note: The Conservation of Matter is further discussed in the next slide.

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SLIDE CHEM-1-4

  • This slide presents a simple demonstration to graphically illustrate Conservation of Matter.
  • When the valve is opened on the upper reservoir, the blue liquid flows into the flask below. At any point in the process, the fluid is either in the reservoir or the flask. But the total amount of the fluid will always be exactly the amount that was present at the beginning.
  • No additional fluid is introduced in the process. In the end, all of the fluid that was in the reservoir ends up in the flask.
  • This is analogous to the situation of any given atom in a chemical reaction. The exact amount of atoms in the reactants must also be present in the reactants – no less and no more.
  • If more atoms were to be present in the products than in the reactants, the matter would have been created from nowhere! If fewer atoms were present in the products than in the reactants, the matter would have been destroyed.
  • The Law of Conservation of Matter tells us that neither of these two things can happen. Matter can neither be created or destroyed.

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SLIDE CHEM-1-5

Note: This slide is used to refresh your memory of several types of evidence that a chemical reaction has occurred. You will likely have seen this slide in previous CELLs.

  • Remember these three forms of evidence that a chemical reaction has occurred.
  • All three forms will be used in the three Investigations of this CELL.

Note: In this Investigation, you will follow a chemical reaction by the heat it releases. Gas formation and color change will be studied in Investigation 2 and Investigation 3, respectively.

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SLIDE CHEM-1-6

 

  • This slide presents the chemical reaction that you will perform in the Lab. The equation for the reaction is as follows:

NH4OH + HCl -> H2O + NH4Cl

  • This is an exothermic reaction. That is, it releases heat as the reaction takes place.
  • You will measure the amount of heat released from the reaction using a simple Styrofoam calorimeter.

Note: Calorimeters can be much more sophisticated and accurate than the simple one your group will make and use in this Investigation. 

  • The red line depicts the addition of ammonium hydroxide (a reactant) to the calorimeter.
  • The second red line depicts the addition of hydrochloric acid (a reactant) to the calorimeter.
  • You should follow the reaction by monitoring heat production.

Note: As an aid, accounting of the individual atoms in the reaction is shown below: 

NA4OH

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SLIDE CHEM-1-7

  • This final slide accentuates the caution that must be taken when working with caustic chemicals such as hydrochloric acid.
  • Lab coats, safety glasses, and gloves should be worn throughout this Investigation.
  • You must wear your safety glasses or goggles to protect your eyes, not resting on the top of your head or dangling around your neck. Just as there is no time to quickly put on a seatbelt in a car just before an accident, there is no time to quickly put on goggles or safety glasses when acid is splashed or another lab accident takes place! Always be safe.

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