Experiment 15a: H & T Lab 3,  Heat Transfer II

 

What have we done and why?  We've demonstrated experimentally that the rise in temperature of a substance is a function of 3 things, the amount of heat input, the mass  of the substance and the specific heat capacity of the substance.  In fact, we've developed the functional relationship, namely, Q = mcDt, where c is the specific heat capacity of the substance.  In the following exercises, cups A and B will contain water at room temperature.  The mass and final temperature of the water is as indicated in the cup in each situation.  

 

You are going to first try to figure out which cup should require the most heat input analytically, then actually perform the experiment and see if your calculations are correct.


Pre-Lab

 

Situations 1 through 3 refer to two cups of water, A and B.  The cups are placed in a room where the temperature is _______oC.

______1.         The water in both cups was initially at room temperature.  Cup A was heated to 75ūC and cup B was heated to 50oC.  Which cup had more heat energy transferred to it?  If they both had the same amount, say they both had the same amount of heat added.

                                   

______2.         The water in both cups was initially at room temperature.  Cup A was heated to 60ūC and cup B was heated to 90oC.  Which cup had more heat energy transferred to it?  If they both had the same amount, say they both had the same amount of heat added.

______3.         The water in both cups was initially at room temperature.  Cup A was heated to 45ūC and cup B was heated to 50oC.  Which cup had more heat energy transferred to it?  If they both had the same amount, say they both had the same amount of heat added.

______4.         Cup A contains 100 grams of water and is initially at 10oC in a refrigerator.  Cup A is heated until its temperature is 30oC.  Cup B contains 80 grams of water initially at 70oC in an oven.  Cup B is heated until its temperature is 90oC.  Which cup had more heat energy transferred to it?  If they both had the same amount, say they both had the same amount of heat added.

_____5.           Cup A contains 100 grams of water at 0oC and cup B contains 100 grams of water at 50oC.  The contents of the two cups are mixed together in an insulated container (no heat can transfer in or out).  The final temperature of the water in the container is

                        A)        Lower than 0oC                                  E)  Between 25oC and 50oC

                        B)        0oC     F) 50oC

                        C)        between 0oC and 25oC           G)  Higher than 50oC

D)            25oC

 

_____6.           Cup A again contains 100 grams of water at 0oC but cup B now contains 200 grams of water at 50oC.  The contents of the two cups are mixed together in an insulated container (no heat can transfer in or out).  The final temperature of the water in the container is

 

                        A)        Lower than 0oC                                  E)  Between 25oC and 50oC

                        B)        0oC     F) 50oC

                        C)        between 0oC and 25oC           G)  Higher than 50oC

D)            25oC

 

Now we'll actually obtain the amount of Qin in each of the situations 1 thru 4, and the final temperature of  the water in situations 5 and 6, and compare these answers with our predictions.


Experiment 14:  H & T Lab 3 Procedure

Start Logger Pro and Set the time scale 0 to 500 seconds.

 

Situation 1:  Record your experimental values, which will be slightly different from those in the figure.

Cup

mass(g)

To

Tf

Dt

V

I

Qin=VIDt

Q= mcDT

A

 

 

 

 

 

 

 

 

B

 

 

 

 

 

 

 

 

Was the experimental values of Q higher or lower than calculated values Q = mcDT ?

 

Can you explain the difference?

Situation 2:  Record your experimental values, which will be slightly different from those in the  figure.

Cup

mass(g)

To

Tf

Dt

V

I

Qin=VIDt

Q= mcDT

A

 

 

 

 

 

 

 

 

B

 

 

 

 

 

 

 

 

 

Was the experimental values of Q higher or lower than calculated values Q = mcDT ?

Can you explain the difference?

Situation 3:  Record your experimental values, which will be slightly different from those in the  figure.

Cup

mass(g)

To

Tf

Dt

V

I

Qin=VIDt

Q= mcDT

A

 

 

 

 

 

 

 

 

B

 

 

 

 

 

 

 

 

Was the experimental values of Q higher or lower than calculated values Q = mcDT ?

Can you explain the difference?

Situation 4:  Record your experimental values, which will be slightly different from those in the figure.

Cup

mass(g)

To

Tf

Dt

V

I

Qin=VIDt

Q= mcDT

A

 

 

 

 

 

 

 

 

B

 

 

 

 

 

 

 

 

Was the experimental values of Q higher or lower than calculated values Q = mcDT ?

 

Can you explain the difference?

Situation 5:  Cup A contains 100 grams of water at 0oC and cup B contains 100 grams of water at 50oC.  The contents of the two cups are mixed together in an insulated container (no heat can transfer in or out).  Calculate the theoretical final temperature of the water in the container.   Use your experimental values of T for A and B in this calculation.

Record your experimental values, which will be slightly different from those in the problem.

Cup

Mass (g)

To

Tf

Tpredicted

A

 

 

 

 

B

 

 

 

 

 

Discuss the descrepancy (or the lack thereof) between the Tf and Tpredicted.

Situation 6:  Cup A again contains 100 grams of water at 0ūC but cup B now contains 200 grams of water at 50ūC.  The contents of the two cups are mixed together in an insulated container (no heat can transfer in or out).  The final temperature of the water in the container is:

Record your experimental values, which will be slightly different those in the problem.

Cup

Mass (g)

To

Tf

Tpredicted

A

 

 

 

 

B