Calorimetry

Introduction

Heat is a form of energy that can pass spontaneously from an object at a higher temperature to an object at a lower temperature – so long as the objects are in physical contact. Heat is also released or absorbed during physical phase changes and during chemical reactions, in which case the heat change (at constant pressure) of the substances in the reaction is known as enthalpy.

In the attached youtube video, https://www.youtube.com/watch?v=8gHFaL2990U, we will quantify the transfer of heat from a hot piece of metal to water at room temperature. Heat transferred to the water (qwater) is given by the equation: qwater = swater · mwater ·∆Twater where m is the mass of water in units of grams (g), ∆T is the change in temperature of the water in ºC, and s is the specific heat of water, which has a known value of 4.184 Joules/(g·°C). Therefore, we need only measure the mass and temperature change of the water in the calorimeter in order to calculate qwater.

Heat transferred from the metal is likewise given by the equation: qmetal = smetal · mmetal ·∆Tmetal The amount of heat absorbed by the water is equal to the amount of heat transferred from the metal. Therefore, we can say: qwater = – qmetal. We can therefore determine the specific heat of the metal, smetal , given that all the values of the other five terms are known.

smetal = (-qwater)/[( mmetal)(∆Tmetal)]

PART 1 Determining the specific heat of a metal:

Please watch the following video https://www.youtube.com/watch?v=8gHFaL2990U

Use the data from the video the calculate the specific heat of the metal knowing that:

qwater = – qmetal

qwater = swater · mwater ·∆Twater where m is the mass of water in units of grams (g), ∆T is the change in temperature of the water in ºC, and s is the specific heat of water, which has a known value of 4.184 Joules/(g·°C). smetal = (-qwater)/[( mmetal)(∆Tmetal)]
Mass of metal __________ g

Volume of water

Mass of water __________mL

__________g

Specific Heat of Water 4.184 Joules/(g·°C)

Initial temp of Water __________·°C

Initial temp of Metal __________·°C

Final temp of Metal/Water __________·°C

Change in temp of water (final – initial) Show calculation __________·°C

Change in temp of metal (final – initial) Show calculation (be careful of signs) __________·°C

q water show calculation _________J

Smetal

Show calculation __________ Joules/(g·°C)

Metal is Cd – True c of cadmium https://www.engineersedge.com/materials/specific_heat_capacity_of_metals_13259.htm 0.2303 J/(g.oC)

Metal is Cd

% Error [(True-Exp)/True ] *100 __________%

PART 2

In the lab simulation, http://chemcollective.org/activities/autograded/117, we will measure the heat of reaction when an ionic salt is dissolved in water.

Some dissolutions are exothermic (give off heat) and others are endothermic (absorb heat).

Heat change = (c- solution * m-solution * ∆T-solution);

In this experiment we use 4 salts: MgSO4, K2SO4, KNO3 and NH4NO3. Calculate the experimental heat of solution for each. Using the number of moles of each, calculate the experimental enthalpy of each. Calculate the theoretical enthalpy of each based off a decomposition reaction such as :

MgSO4 (s) > Mg+2 (aq) + SO4-2 (aq) using the formula such of the products – sum of the reactants and the theoretical values for each enthalpy listed in the text book or online.

Follow the instructions below to gather the data needed for calculations. http://chemcollective.org/activities/autograded/117

Weigh out the salt into a weighing boat. 2- 3 grams is sufficient.

Tare weigh boat.

Add salt.

Add beaker and water. Insulate the beaker.

Add 100 mL of water to the 600 mL beaker.

Pour water into Styrofoam cup

Record the temperature

Add salt to water in foam cup and dissolve. Record final temperature and volume of solution in the foam cup.

Repeat this experiment for the other 3 salts and fill in the table below

Salt

Mass of Salt

Mass of Water Initial

temperature Final temperature Temperature difference

∆T = Tfinal – Tinitial

1 MgSO4

2 K2SO4

3 KNO3

4 NH4NO3

Temperature difference (∆T from previous table Total mass (m) of mixed solution in grams (density of water 1.00 g/mL) Heat change

(qwater = -qRXN =

-sm∆T)

S = 4.184 Moles of salt Heat change per mole (∆H = q/mol)

1

2

3

4

Your results should be approximately as shown below: