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Use of Calorimeter in Experiments

# Use of Calorimeter in Experiments

A calorimeter is an essential device used in experiments that involve measuring the amount of heat exchanged in chemical reactions, physical changes, or specific heat capacity of materials. The term calorimetry comes from the Latin word “calor,” which means heat, and the Greek word “metry,” which means to measure. Essentially, calorimetry is the science of measuring the changes in energy of a system by observing changes in its heat content.

## Types of Calorimeters

There are several types of calorimeters, but the most common are:

1. **Differential Scanning Calorimeters (DSC)**: They measure differential heat flow between a sample and a reference material under controlled temperature conditions.

2. **Bomb Calorimeters**: Used for measuring the heat of combustion of a particular reaction. Samples are burned in a high-pressure container — the “bomb” — and the released heat is measured.

3. **Coffee Cup Calorimeters**: Also known as constant pressure calorimeters, these are simple devices that maintain constant atmospheric pressure and are commonly used in educational laboratories.

4. **Isothermal Titration Calorimeters (ITC)**: They measure the heat change associated with a chemical reaction as one substance is titrated into another.

## Principles of Calorimetry

The principle that underlies calorimetry is the first law of thermodynamics, which states that energy cannot be created or destroyed, only transformed. When a reaction occurs, energy is transferred to or from the surroundings, typically in the form of heat. By measuring this heat transfer, we can calculate the change in enthalpy (\(\Delta H\)) of the reaction, which is a measure of the energy absorbed or released.

The relationship between heat (\(q\)), mass (\(m\)), specific heat capacity (\(c\)), and the change in temperature (\(\Delta T\)) is given by the formula:

\[ q = mc\Delta T \]

## Applications of Calorimetry in Experiments

Calorimeters are used in a variety of scientific studies, including:

1. **Determining Specific Heat Capacities**: By measuring the heat required to change the temperature of a known mass of a substance, one can calculate the specific heat capacity.

2. **Chemical Reaction Energies**: For enthalpy changes in chemical reactions, the heat exchanged with the surroundings is measured.

3. **Food Industry**: To determine the calorie content of food. The food is burned, and the heat released is measured to compute caloric content.

4. **Biological Studies**: Calorimetry helps in understanding metabolic processes and enzyme reactions by measuring small heat changes in living organisms.

5. **Material Analysis**: Characterizing materials by observing thermal transitions such as melting points, glass transitions, and crystallization energy.

# Problems and Solutions about Use of Calorimeter in Experiments

Let’s explore some typical problems and their solutions involving the use of a calorimeter in various experiments.

**Problem 1:**
You place \( 50.0 \) grams of water at \( 25.0 \degree C \) into a calorimeter. When \( 10.0 \) grams of \( 100.0 \degree C \) steam is added, it condenses and the final temperature of the water becomes \( 30.0 \degree C \). Assuming no heat loss to the surroundings, calculate the heat of vaporization of water. (Note that the specific heat capacity of water is \( 4.18 \, J/g \degree C \)).

**Solution:**
The heat gained by the water (\( q_{water} \)) is calculated as:

\[ q_{water} = m_{water}c_{water}\Delta T_{water} \]
\[ q_{water} = 50.0 \, g \times 4.18 \, J/g\degree C \times (30.0 \degree C – 25.0 \degree C) \]
\[ q_{water} = 50.0 \, g \times 4.18 \, J/g\degree C \times 5.0 \degree C \]
\[ q_{water} = 1045 \, J \]

The heat released by the condensing steam (\( q_{steam} \)) equals:

\[ q_{steam} = m_{steam} \Delta H_{vap} \]

Given that no heat is lost to the surroundings, \( q_{water} = q_{steam} \).

\[ 1045 \, J = 10.0 \, g \times \Delta H_{vap} \]

\[ \Delta H_{vap} = \frac{1045 \, J}{10.0 \, g} \]

\[ \Delta H_{vap} = 104.5 \, J/g \]

So the heat of vaporization of water is \( 104.5 \, J/g \).

**Problem 2:**
A metal with a mass of \( 200.0 \) grams is heated to \( 150.0 \degree C \) and then placed in \( 100.0 \) grams of water at \( 20.0 \degree C \) in a calorimeter. The final temperature of the water is \( 25.0 \degree C \). Calculate the specific heat capacity of the metal.

**Solution:**
The heat lost by the metal (\( q_{metal} \)) is equal to the heat gained by the water (\( q_{water} \)).

\[ m_{metal}c_{metal}\Delta T_{metal} = m_{water}c_{water}\Delta T_{water} \]

\[ 200.0 \, g \times c_{metal} \times (25.0 \degree C – 150.0 \degree C) = 100.0 \, g \times 4.18 \, J/g\degree C \times (25.0 \degree C – 20.0 \degree C) \]

\[ 200.0 \, g \times c_{metal} \times (-125.0 \degree C) = 100.0 \, g \times 4.18 \, J/g\degree C \times 5.0 \degree C \]

\[ c_{metal} = \frac{100.0 \, g \times 4.18 \, J/g\degree C \times 5.0 \degree C}{200.0 \, g \times -125.0 \degree C } \]

\[ c_{metal} = \frac{2090 \, J}{-25000 \, g\degree C} \]

\[ c_{metal} = -0.0836 \, J/g\degree C \]

The negative sign indicates the direction of heat flow (lost by the metal), so the specific heat capacity of the metal is \( 0.0836 \, J/g\degree C \).

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