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5: Experiment 5 - Calorimetry

  • Page ID
    214682
  • Ancillary Documents

    Learning Objectives

    Content:

    • Calorimetry
    • Calorimeter constant
    • Specific heat capacity
    • Heat of neutralization

    Process:

    • Design the calorimetry constant experiment 
    • Use virtual labs to find specific heat capacity of an unknown metal
    • Observe the live data steam and use the data to calculate the heat of neutralization

    Prior knowledge:

     

    Calorimetry is the science of measuring heat flow. Heat is defined as thermal energy flowing from an object at a higher temperature to one at a lower temperature. For example, if you drop a coin into a cup with hot water, the temperature of the coin will go up until it is at the same temperature as the boiling water. This will happen because the coin will be absorbing the heat from the water. 

    Calorimetry is based on the First Law of Thermodynamics that states that energy cannot be created nor destroyed. The heat of neutralization that is lost in the chemical reaction (the system) is gained by the calorimeter and its contents (the surroundings).

    This is an IOT lab, where you will be asked to design the experiment and your TA will perform it while streaming data in real time to a Google Sheet. To make this possible your TA will be using Raspberry Pi and Vernier temperature probe. 

    What is IOT? 

    Evolution of Web:

    Web 1.0 - Read only web
    Web 2.0 - Read and write web
    Web 3.0 - Read, write and execute web
    Web 4.0 - IOT

    IOT stands for Internet of Things. It is a system in which devices are talking to each other which doesn't require human-to-human or human-to-computer interaction. Simply put, for this lab your TA can set everything up and walk away while the Raspberry Pi will talk to Google Sheets on its own and stream data. IOT devices can be programmed for virtually anything! 

    During this lab your TA will be streaming data to you (one to many), but in the future students might be streaming data to the TA from their home (many to one). Merging science and technology we can achieve great results!

    What is Raspberry Pi?

    The Raspberry Pi is a series of small single-board computers developed in the United Kingdom by the Raspberry Pi Foundation to promote teaching of basic computer science in schools and in developing countries. The original model became far more popular than anticipated, selling outside its target market for uses such as robotics. It now is widely used even in research projects, such as for weather monitoring because of its low cost and portability. It does not include peripherals (such as keyboards and mice) or cases. However, some accessories have been included in several official and unofficial bundles.1


    640px-Raspberry_Pi_4_Model_B_-_Side.jpg
    Figure \(\PageIndex{1}\): Raspberry Pi (Miiicihiaieil  Hieinizilieir / Wikimedia CommonsCC BY-SA 4.0)

    When someone says "Computer", you probably don't immediately imagine Raspberry Pi, but despite its small size and low cost Raspberry Pi is totally capable of doing anything you’d expect your desktop computer or laptop to do, like browsing the internet, playing high-definition video, programming, making spreadsheets, word-processing, or even playing games! In our case we will use it to stream experiment data.

    Heat Transfer

    Almost all of the chemical reactions are exothermic or endothermic. You can say that the reaction is exothermic if energy or heat is released to increase the temperature of the surroundings. Nitroglycerin exploding is an extremely exothermic reaction. During an endothermic reaction energy or heat is absorbed to decrease the temperature of the surroundings. Cold packs that are used to reduce swelling often use chemicals that when mixed produce an endothermic reaction. 

    Under constant pressure the heat of the reaction is equal to the enthalpy change for the reaction (ΔHΔ).  ΔH is usually reported in units of kilojoules (kJ) per mole of the reactants. The sign of the enthalpy change indicates whether the reaction is exothermic or endothermic.

    • If ΔH is negative, the reaction is exothermic.
    • If ΔH is positive, the reaction is endothermic.

    The heat of the reaction cannot be measured directly, however, if the  reaction is contained in a calorimeter the heat transfer can be calculated. In that case it can be determined by measuring the temperature change ΔT for the contents of the calorimeter and using their specific heat - the heat required to raise the temperature of 1 gram of the substance by 1°C.

     

    ΔT = Tfinal−Tinitial

    q = mcΔT

    where mm is the mass of the substance and cc is the specific heat capacity of a substance. You can find specific heat capacity for different substances in Table 5.2.1 on this page

    ΔTΔT will determine the sign of the heat of the reaction (qq). If ΔT is positive, qq is positive and the reaction is exothermic. If ΔT is negative, qq is also negative and the reaction is endothermic.

    Since you already know that according to the First Law of Thermodynamics qC+qH=0, so qC=−qwe can say that 

     

    mCcCΔT+ mHcHΔTH=
    so

    mCcCΔT= −mHcHΔTH

    where 
    ΔT= Tfinal−TH    and   ΔT= Tfinal−TC

    Calorimeter Constant

    Calorimeters can be different colors, shapes and sizes, but they all have the same application - to measure the change in temperature. You can measure the heat of chemical reactions or physical changes as well as heat capacity. For this remote lab we will be using a calorimeter that you can buy online. 


    IMG_7788.jpg
    Figure \(\PageIndex{2}\): Calorimeter

    In the ideal world, we would have a calorimeter that is so well insulated, that all of the heat gained or lost during the reaction is contained inside the calorimeter completely. You can read more about the heat transfer in an ideal calorimeter here. In reality some of it "escapes", since the calorimeter we have isn't a perfect insulator. Our calorimeter will absorb and lose heat. Keep that in mind when you design your experiment. 

    To make sure you get accurate results you need to calculate the calorimeter constant, which is the calorimeter's heat capacitance. We use capital CC to represent the heat capacitance of an object, so for the calorimeter constant we will use CcalCcal. Calorimeter constant has to me measured for every calorimeter and this is going to be the first part of this lab. 

    If we look at the equation qcold=−qhot  and apply it to our real calorimeter we will see, that there are two cold objects that contribute to qcoldqcold - the cold substance and the calorimeter itself. This means that

     

    qcold = mcoldccoldΔTcold + CcalΔTcold
    or
    qc= mcccΔT+ CcalΔTc        

    Heat of neutralization 

    As been mentioned before, reactions can be exothermic and endothermic. In case of the neutralization reaction where an acid and a base react to neutralize each other you have an example of an exothermic reaction. For example, if a dilute solution of a strong acid (HCl) is reacted with a dilute solution of a strong base (NaOH), the reaction is written

     

    HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) + heat

    The heat of neutralization is defined as the heat transferred when one mole of an acid reacts with one mole of a base. For this lab we will not use a one mole solution of the acid and the base. You will need to calculate the molar heat of neutralization which can be calculated from the heat evolved and the number of moles of water produced in the reaction. Since the reaction mixture gains heat, the change in temperature will have a positive sign. For this experiment we will assume that this solution is so dilute that its specific heat capacity and its density are the same as for water.

    One problem that you will run into during this experiment is that while the temperature is increasing some heat is already being lost to the surroundings which causes the maximum measure to not be as high as it should be. To help with this you will use the graph to determine an acceptable value for the temperature change. According to previous experiments in calorimetry, the most accurate value for the change in temperature should be graphically determined at the time that the temperature rise is 60% of the maximum temperature rise. 

    Procedure

    Make copies of your assignments for this lab by clicking on Google Docs links in Ancillary Documents section above.

    June 8, 2020

    In the ideal world, we would have a calorimeter that is so well insulated, that all of the heat gained or lost during the reaction is contained inside the calorimeter completely. You can read more about the heat transfer in an ideal calorimeter here. In reality some of it "escapes", since the calorimeter we have isn't a perfect insulator. Our calorimeter will absorb and lose heat. Keep that in mind when you design your experiment. 

    To make sure you get accurate results you need to calculate the calorimeter constant, which is the calorimeter's heat capacitance. We use capital \(C\) to represent the heat capacitance of an object, so for the calorimeter constant we will use \(C_{cal}\). Calorimeter constant has to be measured for every calorimeter and this is going to be the first part of this lab. 

    If we look at the equation \(q_{C} = - \;q_{H}\) and apply it to our real calorimeter we will see, that there are two cold objects that contribute to \(q_{C}\) - the cold substance and the calorimeter itself. This means that

    \[Q_H=m_Hc_H \Delta T_H \\ and \\ Q_c=m_cc_c \Delta T_c + C_{cal} \Delta T_c\]

    where Ccal is the heat capacitance of the calorimeter.

    The heat lost by the hot object is gained by the cold.

    \[ Q_c \; =\; -Q_H \\ (m_cc_c \Delta T _c + C_{cal} \Delta T _C) = \; -m_Hc_H \Delta T_H \]

    solving for Ccal:

    \[C_{cal}= \frac{-\;m_cc_c \Delta T _c \;-\; m_Hc_H \Delta T_H}{\Delta T _c}\]

     

    Work with your group in Zoom Breakout Rooms to prepare your Experiment Design Proposal. 

    Interactive Element

     

    June 9, 2020

    Work with your group in Zoom Breakout Rooms to find specific heat capacity of an unknown metal. This is an individual assignment, but you can discuss it with your group members. 

     

    Interactive Element

     

    June 10, 2020

    During this lab you will first access the Google Sheet (link is in your Lab Report), the TA will perform the experiment and stream data directly to the Google Sheet. The data points will be added to the graph automatically. You need to copy the Google Sheet with the data and the graph, add a trendline and find TH and TC from the graph. Take a screenshot of your graph (make sure it has all necessary elements) and include it in your Lab Report.

    Interactive Element

    Interactive Element

    Contributors and Attributions

    Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry). The breadth, depth and veracity of this work is the responsibility of Robert E. Belford, rebelford@ualr.edu. You should contact him if you have any concerns. This material has both original contributions, and content built upon prior contributions of the LibreTexts Community and other resources, including but not limited to:

    • Elena Lisitsyna
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