Thermochemistry: Calorimetry Heat of Neutralization Activities

Activity 1.1: Predictions. Do not perform any experiment or simulations during this activity.

For each task, please provide an answer and an explanation BEFORE doing the experiment.

 

If we mix 300 mL of 1.0 M HCl and 300 mL of 1.0 M NaOH in a calorimeter what will happen to the temperature? Initially, the solutions have the same temperature.

Prediction: increase decrease stay the same

Explain.

 

If we double the volume of each solution, keeping the concentration of each solution at 1.0 M, and mix the solutions what will happen to the temperature? Initially, the solutions have the same temperature.

The change in temperature will _____________ compared to the change in temperature in the first activity.

Explain.

 

Have a staff member check your reasoning. _________

 

Activity 1.2: Use the heat of neutralization simulation located at:

Mix 300 mL of 1.0 M HCl and 300 mL of 1.0 M NaOH in a calorimeter. Be sure to record the initial temperature of each solutions. Mix the solutions. Record the final temperature of the resultant solution. What is the change in the temperature, 慎?

If you double the volume of each solution, keeping the concentration of each solution at 1.0 M, and mix the solutions what will be the change in temperature? Be sure to record the initial temperature of each solution. Mix the solutions. Record the final temperature of the resultant solution..

The change in temperature _____________ compared to the change in temperature in the first experiment.

 

Mix 300 mL of 0.5 M HCl and 300 mL of 0.5 M NaOH in a calorimeter what will be the change in temperature? Be sure to record the initial temperature of each solution. Mix the solutions. Record the final temperature of the resultant solution..

The change in temperature _____________ compared to the change in temperature in the first experiment.

Explain.

Have a s

taff member check your reasoning. _________

Activity 1.3. We will be doing several experiments involving mixing acids and bases to investigate factors that influence the change in temperature. List the factors you think are important to investiate.

Write two questions that you want your experiments to answer.

 

Design your first experiment. Write an outline of what you will do.

What question are you asking?

 

What is the dependent variable? ________________

What is the independent variable? _______________

What variables will you keep constant? ________________________________________

What assumptions do you need to make?

 

 

What pattern or relationship are you looking for? Be able to draw a graph of the relationship.

 

 

 

Have a staff member check your reasoning. _________

 

Once approved, write the question you will address and an outline of the experiment that will ansawer the question on the board. Check to see if you can combine data with another group.

Experiment 1. Do your experiment and collect the data. Put your data and resulting graph on the board.

 

Discuss what you did with another group. Have a staff member listen to a portion of your discussion..

 

Section 2. Heat and heat transfer

Physical processes

When two objets of different temperatures are placed in contact with each other in an insulted container, eventually the two objects will achieve the same temperature (known as thermal equilibrium). We say there is a transfer of heat from the hot object to the cooler object.

 

Explain the difference between heat and temperature.

Have a staff member check your reasoning. _________

What do you use to measure temperature? __________________________

 

How do we determine how much heat has been transferred between two objects of different temperature?

 

Activity 2.1. For example, If you mix 50.0 g of water initially at 20.0°C with 50.0 g of water initially at 10.0°C in an insulated calorimeter, what will be the temperature of the resultant solution?

 

Show all work you do to obtain your answer.

What assumptions, if any, do you need to make?

 

What relationship do you use?

 

What law(s ) do you use?

 

What gains heat? ___________________ What is qgain? ___________________

 

What loses heat? _____________________ What is qloss? ___________________

 

How does this transfer of heat occur?

 

 

 

Have a staff member check your reasoning. _________

 

Chemical processes

We can do the same analysis for chemical processes. Unlike the physical process you just worked with, here we start with two solutions that have the same temperature! When you mixed an acid with a base there was a change in temperature.

Activity 2.2. Choose one of your acid-base experiments to analyze in detail.

The resultant solution and the initial solutions are mostly ____________________. What assumptions, if any, can you make about the resultant solution and the initial solutions?

 

 

 

Do you need to make any other assumptions?

 

 

What gains (absorbs) heat? ___________________ What is qsoln or qgain? ___________________

 

What is the heat of solution?

 

 

 

Have a staff member check your reasoning. _________

What relationship do you use?

What law(s ) do you use?

 

 

Is the acid-base reaction carried out in a calorimeter an open or a closed environment (in theory)?

 

Given the assumptions, theoretically, does any heat from this experiment get to the universe?

 

What is the system?

 

What are the surroundings?

 

Is there a limiting reagent present? If so, what is it? How do you know?

 

 

 

Write a balanced chemical reaction that represents this process.

 

 

 

 

Does this chemical reaction have mass?

 

 

What does the chemical reaction do with respect to temperature? What is the initial and what is the final temperature of the chemical reaction?

 

What does the chemical reaction do with respect to energy?

 

 

What loses (releases) heat? _____________________

 

What is qrxn or qloss? ___________________________. How do you know? What do you have to do in order to get this value?

 

 

 

How much heat was transferred?

 

How does this transfer of heat occur?

 

 

What is the heat of reaction? Is the heat of reaction the system or the surroundings?

 

 

Is the heat of reaction for your acid-base reaction an exothermic or endothermic process?

 

 

 

Have a staff member check your reasoning. _______________

 

In order to make a fair comparison of heat generated or absorbed by chemical reactions, we should calculate energy transfers on a per mole of limiting reactant basis.

 

Experiment 2. Design your second experiment. One variable that you need to investigate is the heat of solution. Write an outline of what you will do.

What question are you asking?

 

What is the dependent variable? ________________

What is the independent variable? _______________

What variables will you keep constant? ________________________________________

What assumptions do you need to make?

 

 

 

What pattern or relationship are you looking for? Be able to draw a graph of the relationship.

 

 

 

 

 

 

 

 

Have a staff member check your reasoning. _________

 

Once approved, write the question you will address and an outline of the experiment that will ansawer the question on the board. Check to see if you can combine data with another group.

 

Do your experiment and collect the data. Put your data and resulting graph on the board.

 

Activity 2.3. Graph

 

Plot a graph to show a relationship between the heat of solution (or heat of reaction) and moles of substance that react.

 

 

Section 3. Change in enthalpy, 食

If the pressure does not change while you are doing your calorimeter experiments, then

qp /mol of limiting reagent = 食 (at constant pressure)

食 is the change in enthalpy. Define 食 in your own words.

 

 

Activity 3.1. Choose one of your acid-base experiments and answer the following questions:

 

Write a balanced chemical reaction for your experiment.

 

 

Is there a limiting reagent in this problem? If so, how many moles of LR react?

 

 

What is releasing heat and what is absorbing heat? What about the sign for heat released and heat absorbed? What do the signs indicate?

______________ Joules are released by __________.

 

______________ Joules are absorbed by _________.

 

What is the heat of reaction, qrxn, in units of Joules for your reaction?

 

 

Determine the change in enthalpy for this reaction (食rxn) in units of kJ/mole. What assumption must you make in order to calculate this value?

 

 

 

Activity 3.2. Determine the change in enthalpy for this reaction (食rxn) in units of kJ/mole using Hess's Law and standard enthalpies of formation data. Compare this value to your experimental value.

 

 

 

 

Activity 3.3. If you double the volume of both acid and base solutions used, what will happen to the "change in enthalpy"of the reaction (食rxn)? Show your work.

increase stays the same decrease

 

 

Activity 3.4. If you use different acid and base solutions, what will happen to the "change in enthalpy"of the reaction (食rxn)? Show your work.

increase stays the same decrease

 

********

Problem #4. A piece of magnesium metal having a mass of 1.22 grams is placed in 100.0 mL of 6.00 M HCl which is in a calorimeter that has a hole in the lid. The initial temperature of the Mg and HCl is 23.0°C. The density of the 6.00 M HCl is 1.10 g/mL. The resultant solution is stirred a bit. The temperature of the resultant solution is recorded every second. The maximum temperature of the resultant solution is 43.5°C. Assume that the specific heat of the resultant solution is 4.18 J/g°C. Calculate the heat of reaction. Calculate 食 for this reaction using the above experimental values. Calculate the 食 for this reaction using standard enthalpies of reaction. Compare.

 

Problem #5. A piece of magnesium metal having a mass of 1.22 grams is placed in 100.0 mL of 6.00 M HCl which is in a calorimeter. All other conditions mentioned in the previous problem apply. What do you expect for the change in temperature? Calculate the heat of reaction. Calculate 食 for this reaction using the above experimental values. Compare the 食 for this reaction with the previous experiment.

 

Problem #7. A 50.0 mL sample of 0.400 M copper(II) nitrate solution at 23.35°C is mixed with 50.0 mL of 0.600 M sodium hydroxide solution, also at 23.35°C, in a coffee-cup calorimeter. After the reaction occurs, the maximum temperature of the resultant solution is measured to be 25.23°C. The density of the resultant solution is 1.02 g/mL. Assume that the specific heat of the resultant solution is 4.184 J/go°C. Calculate the heat associated with the chemical reaction. Calculate 食 for this reaction.

 

Problem #8. A 100.0 mL sample of 0.400 M copper(II) nitrate solution at 23.35°C is mixed with 100.0 mL of 0.600 M sodium hydroxide solution, also at 23.35°C, in a coffee-cup calorimeter. The density of the resultant solution is 1.02 g/mL. Assume that the specific heat of the resultant solution is 4.184 J/go°C. What is the maximum temperature of the resultant solution? Is the maximum temperature of the resultant solution greater than, less than or the same as the previous experiment? Compare the heat associated with the reaction in this experiment to the previous experiment. Compare the 食 for this reaction with the previous experiment.