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The African bombardier beetle (Stenaptinus insignis) can emit a jet of defensive spray from the movable tip of its abdomen (Fig. \(\mathbf{P 1 7 . 9 1}\) ). The beetle's body has reservoirs containing two chemicals; when the beetle is disturbed, these chemicals combine in a reaction chamber, producing a compound that is warmed from \(20^{\circ} \mathrm{C}\) to \(100^{\circ} \mathrm{C}\) by the heat of reaction. The high pressure produced allows the compound to be sprayed out at speeds up to \(19 \mathrm{~m} / \mathrm{s}(68 \mathrm{~km} / \mathrm{h}),\) scar- ing away predators of all kinds. (The beetle shown in Fig. \(\mathrm{P} 17.91\) is \(2 \mathrm{~cm}\) long.) Calculate the heat of reaction of the two chemicals (in \(\mathrm{J} / \mathrm{kg}\) ). Assume that the specific heat of the chemicals and of the spray is the same as that of water, \(4.19 \times 10^{3} \mathrm{~J} / \mathrm{kg} \cdot \mathrm{K}\) and that the initial temperature of the chemicals is \(20^{\circ} \mathrm{C}\).

Step by step solution

01

Identify Given Information

In the exercise, the following information are given: \n\n The initial temperature, \(T_{i} = 20^{\circ} \mathrm{C}\) or in Kelvin, \(T_{i} = 20 + 273 = 293 \, K\)\n The final temperature, \(T_{f} = 100^{\circ} \mathrm{C}\) or in Kelvin, \(T_{f} = 100 + 273 = 373 \, K\)\n The specific heat capacity, \(c = 4.19 \times 10^{3} \, J / kg \cdot K\)

02

Calculate Temperature Change

The change in temperature can be calculated by subtracting the initial temperature from the final temperature. \n\n That is, \n\n \(\Delta{T} = T_{f} - T_{i} = 373 \, K - 293 \, K = 80 \, K\)

03

Calculate The Heat of Reaction

Assuming the mass of the chemicals to be one kilogram, one can apply the heat equation \(Q = mc\Delta{T}\) to find the heat of the reaction.\n\n Here, \n\n\(Q = (1 \, kg)(4.19 \times 10^{3} \, J / kg \cdot K)(80 \, K) = 3.35 \times 10^{5} \, J\)\n\n The heat of reaction of the two chemicals per kg is \(3.35 \times 10^{5} J/kg \)

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Bombardier Beetle

The African bombardier beetle, known scientifically as Stenaptinus insignis, is a fascinating creature. This small beetle possesses an impressive defense mechanism that involves the ejection of a hot, noxious spray. When threatened, the beetle releases this spray from the tip of its abdomen. The spray consists of chemicals stored in separate reservoirs within its body. These chemicals mix in a reaction chamber, which leads to an explosive release of heat and pressure.
The high-pressure spray travels at speeds up to 19 meters per second (or 68 kilometers per hour). This startling burst can effectively deter predators and ensure the beetle's safety. The beetle is only 2 centimeters long, yet it wields this powerful defense mechanism. Studying the bombardier beetle provides insights into natural chemical processes and has even inspired technological innovations in human industries.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, transform into new substances called products. The bombardier beetle's defense spray is a perfect example of a rapid and exothermic chemical reaction, which means it releases heat.
In the beetle, specific chemicals are stored separately to prevent premature reactions. Upon mixing in the reaction chamber, these chemicals undergo a series of reactions that generate heat and pressure, leading to the ejection of the spray.
Understanding chemical reactions is crucial as they form the basis of countless processes in nature and human activities. Features of a reaction include:

• Change of temperature
• Emission or absorption of heat
• Formation of new products
• Change of color

Learning about chemical reactions helps students grasp not only biological processes but also applications in chemistry and other sciences.

Specific Heat Capacity

Heating involves energy transfer, related to the concept of specific heat capacity. The specific heat capacity is the amount of heat required to raise the temperature of one kilogram of a substance by one Kelvin (or one degree Celsius).
In the bombardier beetle exercise, we assume that the chemicals in the reaction have a specific heat capacity equivalent to that of water, which is 4.19 x 10鲁 J/kg路K. This means that for every kilogram, raising the temperature by one Kelvin requires 4.19 x 10鲁 joules of energy.
This concept is vital in thermochemistry as it helps to understand how substances respond to heat. Different substances have different specific heat capacities, which influence how they undergo temperature changes during chemical reactions. Specific heat capacity applies to various scientific fields,

Heat of Reaction

The heat of reaction, also known as enthalpy change, is the heat energy absorbed or released during a chemical reaction. For the bombardier beetle, the reaction heats the spray from 20掳C to 100掳C.
In studies, the heat of reaction is calculated by using the formula: \[ Q = mc\Delta{T} \]where \( Q \) is the heat energy, \( m \) is the mass, and \( \Delta{T} \) is the temperature change. For this beetle, this amounts to 3.35 x 10鈦� J/kg, indicating a significant energy release per unit mass of chemical reacting.
Heat of reaction is an essential part of thermochemistry, helping to predict whether a reaction will be exothermic (releasing heat) or endothermic (absorbing heat). It provides insights into energy transfer processes and is crucial for applications in various scientific fields, such as energy production and material synthesis.