SPECIFIC HEAT LAB - Mrs. Wernau's Pre-AP Chemistry



SPECIFIC HEAT LAB

PRE-LAB DISCUSSION:

The amount of heat required to raise the temperature of a solid body depends on its change in temperature (Delta;T), its mass (m), and an intrinsic characteristic of the material forming the body called specific heat (cp). The heat is calculated from the equation

q = cp x m x ΔT

The unit for cp is thus heat per unit mass per unit temperature. The value of cp does depend on the temperature. However, for the small temperature range we are interested in, it is a good approximation to regard cp as temperature independent. Historically, heat (q) was measured in terms of calories. The calorie was defined as the amount of heat required to raise the temperature of 1 gram of water by 1 ºC from 14.5 ºC to 15.5 ºC at 1 atmosphere pressure. With this definition, the specific heat of water is 1.00 cal/(g · ºC). The use of the calorie began before it was established that heat is a form of energy and 1 calorie is equivalent to 4.18 J. The joule (J) has become the more favored unit in recent years. Thus, the units for cp that we will use are J/(g · ºC). The specific heat of water is then 4.18 J/(g · ºC).

PURPOSE:

To apply the experimental methods of calorimetry in the determination of the specific heat of a metal.

PROCEDURE:

1. Go to the following URL:

2. Use the Flash lab animation to make measurements on the six materials provided.

3. Perform three trials for EACH material. Record the mass of the sample, the initial temperature (T1), the final temperature (T2), and the energy absorbed (in joules).

4. Vary the mass of the sample and the length of time heating for each trial with a given material. In other words, no two trials for a given material should use both the same mass and the same flame exposure times.

5. At the end of each trial, hit the "Reset" button to prepare for the next trial.

[pic]

Flash simulation courtesy of UMass Chemland Chemistry.

OBSERVATIONS AND DATA:

|Material____________ |Trial #1 |Trial #2 |Trial #3 |

|Mass of object, m (g) |g |g |g |

|Initial temperature of object (T1) |ºC |ºC |ºC |

|Final temperature of object (T2) |ºC |ºC |ºC |

|Energy absorbed (Joules) |J |J |J |

CALCULATIONS: Show your work! You will repeat the calculations three times for each material you test.

1. Calculate the temperature change, ΔT, (T2 - T1).

2. Calculate the specific heat, Cp. Cp = q ÷ m ÷ ΔT

|Material____________ |Trial #1 |Trial #2 |Trial #3 |

|ΔT, (T2 - T1) |ºC |ºC |ºC |

|Cp |J/(g · ºC) |J/(g · ºC) |J/(g · ºC) |

QUESTIONS FOR DISCUSSION

1. What effect, if any, does the mass of the sample and the time spent heating have on the specific heat calculated for each substance?

2. What substance had the highest specific heat of the substances measured?

3. Compared to the other substances, are the specific heats of metals (copper, silver, sodium) higher or lower than the other materials measured (wood, glass, water)?

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