LAB 12: INTRODUCTION TO ENDOTHERMIC AND EXOTHERMIC REACTIONS
- Page ID
- 506053
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)PURPOSE
The purpose of this experiment is to
• Observe various physical and chemical processes and record observations.
• Determine the temperature change of a process.
• Predict whether a process is endothermic or exothermic.
INTRODUCTION
As you have seen throughout the semester, a process can be physical if it produces different forms of the same material or chemical if a new substance is formed. Physical and chemical changes often occur with the transfer of heat energy between the system and surroundings. The system is defined as the chemicals (reactants and products) involved in the process. Everything else, including the glassware containing the chemicals, the lab bench, and those observing the process, constitutes the surroundings. We always discuss heat transfer with respect to the system. A process in which the system absorbs heat energy is called endothermic. In an exothermic process, the system releases heat energy.
Consider the following reaction:
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g)
This is the combustion of methane (CH4), which is used as the gas in some home stoves. This process is exothermic, as it releases heat energy, increasing the temperature of the immediate surroundings.
Next, consider an instant cold pack. When the chemicals inside mix, the system absorbs heat energy, causing a decrease in the temperature of the immediate surroundings, such as the part of the body on which the pack is placed. This is an example of an endothermic reaction.
Physical and chemical changes can be either endothermic or exothermic. In this experiment, you observe and record temperature changes in six processes. You will predict whether the process is endothermic or exothermic based on the temperature change.
SAFETY PRECAUTIONS
1) Always wear chemical splash goggles while working with chemicals in this experiment.
2) Gloves are provided if you wish to wear them.
3) Handle all chemicals carefully and read all labels on reagent bottles to ensure you mix the correct chemicals.
4) Dispose of all waste as directed by your instructor.
5) Clean your work area and return all the chemicals and equipment to the appropriate place when finished.
CHEMICALS and EQUIPMENT NEEDED
• Medium size test tube
• 10 mL graduated cylinder
• 100 mL graduated cylinder
• Spatula
• 50 mL beaker
• 600 mL beaker
• Celsius thermometer
• Coffee cup
• Solid ammonium nitrate
• Solid calcium chloride
• 1 M HCl
• 1 M NaOH
• Water
• Isopropyl alcohol
• Critic acid
• Solid baking soda
• Mg metal
• Non-halogenated organic waste container
• Inorganic waste container.
EXPERIMENTAL PROCEDURE
1) Add 5 mL of isopropyl alcohol to a medium-sized test tube. Place a thermometer in the test tube containing the isopropyl alcohol and record the initial temperature. (When recording temperature, wait for the thermometer reading to stabilize.) Remove the thermometer from the test tube and hold it in the air. You will notice the temperature reading either increases or decreases. Once the temperature reading reaches a maximum or minimum value, record this as the final temperature. Calculate the temperature change by subtracting the initial temperature from the final temperature. Pour the isopropyl alcohol into the non-halogenated organic waste container.
2) Add 20 mL of water to a coffee cup. Record the initial temperature of the water. Using a spatula, add a scoop of solid ammonium nitrate to the water. Gently stir the solution with the thermometer for approximately 30-45 seconds, and then record the final temperature of the solution. Pour the contents of the coffee cup into the inorganic waste container. Clean and dry the coffee cup and other equipment, then set these items aside for steps 3 and 4.
3) Repeat step 2 using solid calcium chloride instead of ammonium chloride.
4) Add 10 mL of 1 M HCl to the coffee cup. Record the initial temperature. In a 50 mL beaker, obtain 10 mL of 1 M NaOH. Pour the NaOH solution into the coffee cup containing the HCl solution and gently stir with the thermometer for approximately 30 seconds. Record the final temperature of the resulting solution. Pour the contents of the coffee cup into the sink, rinsing with plenty of water. Clean and dry the coffee cup and other equipment, then set these items aside for step 5.
5) Add 20 mL of citric acid to the coffee cup. Place the coffee cup in a 600 mL beaker. Record the initial temperature. Add a scoop of baking soda to the citric acid and record the final temperature. Once the final temperature is reached and the reaction is complete, pour the contents of the coffee cup (and 600 mL beaker) into the inorganic waste container. Clean and dry the coffee cup and other equipment, then set these items aside for step 6.
6) Add 20 mL of 1 M HCl to the coffee cup. Place the coffee cup in a 600 mL beaker. Record the initial temperature. Add (approximately) a 10-15 cm strip of Mg metal to the HCl and record the final temperature. Once the final temperature is reached and the reaction is complete, pour the contents of the coffee cup (and 600 mL beaker) into the inorganic waste container. Clean and dry the coffee cup and other equipment. The coffee cup may now be discarded and other equipment returned to the appropriate place.
7) Clean your work area before leaving the lab.
PRE-LAB QUESTIONS Name ____________________________________
1) In your own words, define the following terms:
System:
Surroundings:
Temperature:
Endothermic process:
Exothermic process:
2) What is one way to tell if a process is endothermic or exothermic?
3) When a large scoop of magnesium sulfate is dissolved in a beaker of water at 25 °C, the temperature of the solution rises to 30 °C. Based on this observation, would you predict the dissolution of magnesium sulfate in water to be endothermic or exothermic? Explain.
4) When ice sits at room temperature, it will eventually melt. In this instance, would heat be absorbed or released by the ice? Would this process be endothermic or exothermic?
DATA AND CALCULATIONS
Complete the following table.
|
Process |
Observations of Process |
Initial Temperature |
Final Temperature |
Temperature Change |
Endothermic or exothermic? |
|
Evaporation of Isopropyl Alcohol |
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|
Dissolution of Ammonium Nitrate in water |
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|
Dissolution of Calcium Chloride in water |
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|
Reaction of Hydrochloric Acid and Sodium Hydroxide |
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|
Reaction of Citric acid and Baking Soda |
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|
Reaction of Magnesium and Hydrochloric acid |
POST LAB QUESTIONS
1) What was the biggest takeaway from this activity?
2) Generally, if a process is endothermic in one direction, it is exothermic in the opposite direction. Based on your results from step 1 (evaporation of isopropyl alcohol), would you expect condensation (a physical change in which a gas is converted into a liquid) to be endothermic or exothermic? Explain.
3) Predict whether the processes described below would be endothermic or exothermic.
Part A: When placed in a freezer, water is converted into ice.
Part B: Sodium metal reacts explosively when placed in water.
Part C: When heated, ammonium chloride sublimes (a physical change in which a substance is converted from a solid into a gas).
Part D: An instant hot pack is placed on an athlete’s leg to relieve pain.
4) Give an example of an endothermic and exothermic process (not described in this experiment) that can be seen in everyday life.
5) Initially, when entering a sauna, you may experience a sharp elevation in temperature. Over time, your body will begin to cool before it heats up again. Using what you learned in this experiment, explain why this happens.