Short Notes on Types of Thermal reactions.
Exothermic Reaction –
- negative heat flow
- heat loss to the surroundings (get hot)
- produce heat or can be explosive
- can be spontaneous
Na + Cl à NaCl gives off 411 KJ of energy
Zn + HCl à ZnCl + H2 (corrosion)
How can you tell that a chemical change has taken place?
What problem could result if you put the cork on too tight?
You produced hydrogen gas (what are 4 properties)
How is hydrogen like oxygen?
How is hydrogen different?
Endothermic Reaction –
- must absorb energy to occur
- cannot be spontaneous – work must be done
- absorb heat so reaction “gets cold”
photosynthesis requires 15MJ of energy for 1 kg of glucose (what energy is put into the reaction)
Title: Reaction Demos
Purpose: recognize the parts and importance of chemical equation when describing how things chemically react to form new substances. Identify exothermic and endothermic reaction.
8.9 substances have chemical physical properties
8.10 complex interactions occur between mater and energy
Materials: labeled chemicals, test tubes, test tube rack, goggles, apron
Procedure:
1. On your reaction chart (for each demonstration) place a red box around the reactants and a blue circle around the products.
2. Follow the exact instructions which go along with the chemical reaction. Be sure to wear goggles and aprons at all times. Dispose of wastes properly.
3. Fill in the rest of chart for the chemical reaction. Use your notes if needed to help identify the type (if possible) be sure to provide at least two (2) pieces of evidence for the reaction.
Teacher demo and discussion:
2Zn + 2HCl à 2ZnCl + H2
How many molecules of HCl are in the reactants?
How many atoms of Zn are on the products side of the equation?
4Fe + 3O2 à 2Fe2O3 (rust)
Identify one molecule in the equation.
How many atoms are in one compound of Fe2O3?
Equation / Thermal Type (exo or endo) / Reaction Type (syn, double, single, decomp) / Other Evidence6CO2 + 6H2O àC6H12O6 + 6O2
Photosynthesis is the conversion of light energy into chemical energy by living organisms. The raw reactants are carbon dioxide and water; the energy source is sunlight; and the products include oxygen and (energy rich) carbohydrates, for example sucrose and starch.
Photosynthesis occurs in the plastid, chloroplast. The chloroplast is the green colored organelle found in plant cells. Some plants have different colored pigments in their chloroplast such as red.
2NH4NO3 à 2N2 + O2 + 4H2O
1. Add 10 ml of H2O to the test tube. Add the thermometer and observe the initial temperature.
2. Place 1 scoop of NH4NO3 in the test tube.
3. Gently swirl the test tube.
4. Observe the reaction and fill in your data chart.
5. When finished, pour products through the strainer in the back sink. Place remaining NH4NO3 in the proper container.
6. Clean up when finished and return all materials to the bin.
C6H8O7 + 3NaHCO3à 3CO2+ 3H2O + NaC6H5O7
1. Place 10 ml of C6H8O7 to the test tube. Add the thermometer and observe the initial temperature.
2. Add 1tsp of NaHCO3 to the test tube.
3. Stir or swirl the chemical together.
4. Observe the reaction, including the temperature change. Fill in your data chart.
5. When finished, pour products into the sink.
6. Clean up your lab area and return all materials to the bin.
CaCl2 + 2Na(HCO3) à2NaCl + CO2 + Ca(HCO3)2
1. Measure 2 eye droppers full of C19H1305S and place into the test tube. The phenol red is a combination of C19H1305S powder and water. Phenol Red is an acid base/base indicator. It is generally red in the presence of bases and yellow in presence of acids.
2. Add the thermometer and observe the initial temperature.
3. Put 10 ml of NaHCO3 into the test tube. Add 1 scoop of CaCl2.
3. Gently swirl the contents together.
4. Observe the reaction and write your observations in the data chart.
6. Pour contents into sink.
7. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
2H2O2 ----> 2H2O + O2
In this lab, you will study an enzyme that is found in the cells of many living tissues. The name of the enzyme is catalase (KAT-uh-LAYSS); it speeds up a reaction which breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and oxygen.
This reaction is important to cells because hydrogen peroxide (H2O2) is produced as a waste product (byproduct) of many normal cellular reactions. If the cells did not break down the hydrogen peroxide, they would be poisoned and die. In this lab, you will study the catalase found in liver cells.
It might seem strange to use dead cells to study the function of enzymes. This is possible because when a cell dies, the enzymes remain intact and active for several weeks, as long as the tissue is kept refrigerated.
1. Place 5 ml of H2O2 to a test tube.
2. Place a thermometer in the test tube. Observe the initial temperature.
3. Add a small piece of liver to the test tube.
4. Observe the reaction and write your observations in the data chart.
6. Pour contents into sink.
7. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
Na(OH) + HCl à NaCl +H2O
1. Add 5 ml of HCl to the test tube. Add the thermometer and observe the initial temperature.
2. Put 1 scoop of Na(OH) into the test tube.
3. Gently swirl the contents together.
4. Observe the reaction and write your observations in the data chart.
5. Pour contents into sink.
6. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
NaHCO3 + HOOCCH3 à NaOOCCH3 + H2O + CO2
1. Add 5 ml of HOOCCH3 to the test tube. Add the thermometer and observe the initial temperature.
2. Put 1 scoop NaHCO3 of into the test tube.
3. Gently swirl the contents together.
4. Observe the reaction and write your observations in the data chart.
5. Pour contents into sink.
6. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
Al2(SO4)3 + 6 NaHCO3 → 2 Al(OH)3 + 3 Na2SO4 + 6 CO2
1. Add 5 ml of NaHCO3 to the test tube. Add the thermometer and observe the initial temperature.
2. Put 1 scoop of Al2(SO4)3 into the test tube.
3. Gently swirl the contents together.
4. Observe the reaction and write your observations in the data chart.
5. Pour contents into sink.
6. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
CaCO3 + HCl à CO2 + CaCl2 + H20
1. Put 5 ml of CaCO3 into the test tube.
2. Add the thermometer and observe the initial temperature.
3. Put 10 ml of HCl into the test tube.
3. Gently swirl the contents together.
4. Observe the reaction and write your observations in the data chart.
6. Pour contents into sink.
7. Clean up your lab station and return all materials to the bin. You may need to scrub out the test tube.
CO2 + Ca(OH)2 à CaCO3 + H2O
1. Place 10 ml of Ca(OH)2 to the test tube. Add the thermometer and observe the initial temperature.
2. Add 5 ml of CO2 to the test tube.
3. Stir or swirl the chemical together.
4. Observe the reaction, including the temperature change. Fill in your data chart.
5. When finished, pour products into the sink.
6. Clean up your lab area and return all materials to the bin.
Key for Reactions
Zn + HCl Exothermic, single replacement
Fe + O2 Exothermic, synthesis
Photosynthesis Endothermic, synthesis
NaH4NO3 (ammonium nitrate) Endothermic, decomposition
H3C6H5O7 (citric acid) + NaHCO3 (sodium bicarbonate) Endothermic, Decomposition
CaCl2 (calcium chloride) + NaHCO3 (baking soda) Exothermic, Double replacement
CO2 (from sparkling water)+ Ca(OH)2 (lime water) àCaCO3 + H2O single replacement, white precipitant
Liver and H2O2 peroxide Exothermic, decomposition (enzymatic action)
Na(OH) + HCl > NaCl +H2O double replacement
Lithium chloride + water exothermic (40g LiCl 50ml H2O)
Potassium Chloride + water endothermic
Ammonium chloride + water endothermic
C3H5O(COOH)3 (fruit juice) with ammonia makes a salt?
Al2(SO4)3 + 6 NaHCO3 → 2 Al(OH)3 + 3 Na2SO4 + 6 CO2 Aluminium Sulfate + baking soda endothermic = used for fire extinguishers
Calcium hydroxide in water Ca(OH)2 (lime water) (see above)
CaCO3 + H2O + 2HCl (any acid) à CO2 + CaCl2 + H20 (exothermic?) turns from milky white to clear
Barium chloride and sodium sulfate
Epsom salt and alum
Aluminum and copper chloride
· KCl(aq) + Pb(NO3)2(aq) --> KNO3(aq) + PbCl2 precipitate
The only way you can form a precipitate is if the cation and anion
combination have a very low solubility product. Unfortunately, most
nitrates and carbonates are soluble, and of the chlorides only silver
chloride and lead chloride are insoluble. You may have to get access to
some silver nitrate or lead(II) nitrate - which when combined with the
chlorides should form a precipitate. Alternatively, barium hydroxide and calcium hydroxide are only sparingly soluble - so if you can get a hold of sodium or potassium hydroxide - that would work too.
There are two issues here. The first is safety. Strontium, and Barium can be toxic if ingested so cautious handling and supervision are necessary. Nitrates can also be toxic but to a lesser extent. An interesting precipitation reaction is to take a solution of freshly prepared calcium chloride and have the students exhale, that is, blow bubbles through a soda straw immersed in the calcium chloride solution. Carbon dioxide exhaled from the lungs forms calcium carbonate which causes the solution to turn cloudy. Keep the stock solution of CaCl2 protected from the atmosphere because it will absorb CO2 from the atmosphere. Strontium and barium chloride will undergo the same precipitation reaction, but I would be cautious about handling these salts by 6-8th graders without careful supervision. You could compare the results of exhaling through a solution of Ca(Cl)2 and Mg(SO4) [Epsom's salt] which is available at any pharmacy and most grocery stores. The solubility product constant of Mg(CO3)and Ca(CO3) is 6x10^-6 and 3x10^-9, so the difference in the amount of breath necessary to precipitate the two solutions should be observable, although
I have not done the experiment.
Another demonstration could be done with Ca(CO3). While it is only very slightly soluble in water, you could start with a slurry of the solid and add HCl. This will cause the precipitate to dissolve, and the solution to become clear. Then, raise the pH with KOH (or NaOH). As the solution becomes more alkaline, Ca(OH)2 will precipitate because its solubility product constant is about 5x10^-6.
· Endothermic Reaction
· reaction of barium hydroxide octahydrate crystals with dry ammonium chloride
· dissolving ammonium chloride in water
· reaction of thionyl chloride (SOCl2) with cobalt(II) sulfate heptahydrate
· mixing water and ammonium nitrate
· mixing water with potassium chloride
· reacting ethanoic acid with sodium carbonate
· photosynthesis (chlorophyll is used to react carbon dioxide plus water plus energy to make glucose and oxygen)
Endothermic and Exothermic Reactions
Introduction:
This demonstration illustrates how chemical reaction can either give off heat (exothermic) or absorb heat (endothermic). The crystallization of a supersaturated sodium acetate solution is an exothermic process that is available commercially is the form of hand warmers. This demonstration can also be carried out in a large flask by seeding the supersaturated solution with a small sodium acetate crystal.
To demonstrate an endothermic process, Barium hydroxide (octahydrate) and Ammonium nitrate are mixed (in a 2:1 ratio) in a small beaker. This reaction displays the endothermic process and illustrated the interaction between changes in enthalpy and entropy is spontaneous chemical reactions. For a process to take place spontaneously at constant temperature and pressure, the change in free energy must be negative. An endothermic reaction may thus be spontaneous at constant pressure if the positive value of the heat absorbed is offset by a sufficient increase in entropy (randomness). In the reaction between barium hydroxide octahydrate and ammonium nitrate, the large increase in entropy is related to the increase in the number of particles present and their states (remember that two solids are combining to form a solid product and some liquid). As the reaction below shows, there are three molecules that combine to form 13 product molecules.
With this reaction, temperatures of -20o C can be achieved. Both of these demos can be done hands-on by volunteers from the audience.
Materials:
· Flask of supersaturated sodium acetate
· Sodium acetate seed crystals
· Handwarmers (one for each or every other student)
· Approximately 32g of barium hydroxide octahydrate
· Approximately 17g of ammonium nitrate
· 125 mL Erlenmeyer flask
· Glass stirring rod
· Small piece of cardboard
· Squeeze bottle of water
Exothermic Reactions
Procedure:
Handwarmers can be passed out among the audience (for smaller groups there should be enough for each or at least every other student). Have the student click the metal disk inside the handwarmers to activate the crystallization. They should notice that the crystallization will begin at the metal disk and spread outward though the whole package. As an alternative, the large flask containing the sodium acetate solution can be used. To activate the crystallization, add a single seed crystal of sodium acetate. If the solution has been regenerated properly you should observe a long crystalline spike run out from the seed crystal and eventually spread through the whole solution. As the solution crystallizes, the system will give off heat.