Chem 105a Lab Exam: Experiment #5 (Calorimetry)

What is an adiabatic system?

"isolated system" ~ no energy or matter exchange

Main objective?

To determine the heat capacity of a human hand and the enthalpy of a reaction with a salt to determine which salt to use in a heat pack

What can a closed system exchange?

Can exchange energy but not matter

How does the heat pack with water and a solid powder work?

Once the pouch of water is broken open, there is an exothermic reaction between the water and the powder

specific heat capacity

the amount of heat energy required to raise the temperature of one gram of substance by one degree celcius

All calorimetry experiments are based on the __ Law of Thermodynamics which says...

1st; the total energy of the universe is constant

Equation of heat exchange between water and sausage

m (water) x C (p, water) x delta T (water) = -m (sausage) x C (p, sausage) x delta T (sausage)

For an endothermic reaction, what will happen to the temperature of the calorimeter?

T of calorimeter will decrease

For an exothermic reaction, what will happen to the temperature of the calorimeter?

T of calorimeter will increase

Is the coffee cup calorimeter an adiabatic system?

No, heat will be transferred from the cup to the surfaces around it, and it can transfer matter out of itself

Safety concerns?

Do not eat the Vienna sausages

Salts act as irritants

Why do you let the sausages rest in the ice slush for 10-15 minutes?

To get them to a constant, measurable temperature

Values needed while calculating heat capacity of sausage in lab

Temperature of DI water in cup

Internal temperature of cold sausage

Final temperature of water + sausage solution

mass of sausage

mass of water

Why must you clean and dry the coffee cups in between trials?

So that there is no residual sausage mass

When doing enthalpy tests for the salt, why do you change the amount of water you dissolve the salt in in the 3 different trials?

To measure the average molar enthalpy of the reaction

equation used in salt part of lab to determine molar enthalpy of the reaction

n (salt) x delta H (reaction) = -m (solution) x C (p, solution) x delta T (solution)

Sources of error

Random: spillage of water in the cup, loss of mass during transfer of the sausage or salts, not allowing the heat to completely transfer

Systematic: leaps in the Styrofoam cup, cups being only closed systems (heat transfer), improprerly calibrated thermometers

Which salt was the only salt whose dissolution was exothermic?

MgSO4