Question

Hydrogen and iodine react to give hydrogen iodide while absorbing heat energy. An experiment shows that the total mass of the reactants is equal to the product. In theory, should the product weigh slightly more or slightly less than the reactants?

Short answer

The product should weigh the same as the reactants, according to the conservation of mass.

Step-by-step solution

Understand the Reaction

The reaction between hydrogen and iodine to form hydrogen iodide can be written as: \[ H_2 + I_2 \rightarrow 2HI \]. This is a chemical reaction where heat energy is absorbed, indicating it is endothermic.

Apply the Law of Conservation of Mass

According to the law of conservation of mass, mass is neither created nor destroyed in a chemical reaction. This means that the mass of the reactants (hydrogen and iodine) will be equal to the mass of the products (hydrogen iodide), regardless of energy changes.

Consider the Effect of Energy Absorption

While energy absorption (endothermic process) is involved, it is significant for the energy transfer and system stability but does not affect the mass of substances. The mass remains constant even though energy is absorbed during the reaction.

Conclusion on Product Mass

Based on the conservation of mass and despite the endothermic nature of the reaction, the mass of the products, hydrogen iodide, will be equal to the mass of the reactants. There will be no difference in mass.

Key concepts

Endothermic Reaction

In an endothermic reaction, the system absorbs heat energy from its surroundings. This energy intake is necessary to break bonds in the reactants and allow new bonds to form in the products. A good example is the reaction between hydrogen and iodine to form hydrogen iodide. During this process, energy is absorbed to facilitate the transformation, which is why it's classified as endothermic. However, despite the energy being absorbed, the overall mass of the substances involved in the reaction doesn't change.
Important points to remember about endothermic reactions include:

• Energy absorption leads to a temperature drop in the surroundings.
• Energy absorbed is usually required for bond breaking in reactants.
• This type of reaction often feels cold to the touch.

Endothermic reactions are quite common in chemical processes, and they play a crucial role in fields ranging from energy production to cooking.

Chemical Reactions

Chemical reactions involve the transformation of substances through breaking and forming of chemical bonds. This process leads to the creation of products that have different properties compared to the reactants.
One way to represent a chemical reaction is with a chemical equation, which shows reactants converting into products. For instance, in the equation \[ H_2 + I_2 \rightarrow 2HI \], hydrogen and iodine react to form hydrogen iodide.
Key characteristics of chemical reactions include:

• Reactivity: Not all substances react the same way; reactivity depends on the nature of the substance.
• Indicators of a chemical reaction: These can be changes in color, temperature, the formation of a precipitate, or gas bubbles.
• The ability to balance the chemical equations respects the law of conservation of mass.

Understanding chemical reactions allows scientists and engineers to manipulate chemical processes for innovations and solutions.

Mass-Energy Relationship

The mass-energy relationship is crucial in understanding interactions at the atomic and molecular level. According to the law of conservation of mass, the mass of the reactants in a chemical reaction must equal the mass of the products. Even when energy exchanges occur during the reaction, such as in an endothermic process, the total mass remains unchanged.
This stems from Albert Einstein's famous equation, \[ E=mc^2 \], which shows the interrelation between mass (m) and energy (E) with \( c \) being the speed of light.
However, in everyday chemical reactions, the energy involved is so small compared to \( c^2 \) that any change in mass is negligible and undetectable.
Important points to know about the mass-energy relationship:

• The principle implies mass can convert to energy and vice versa.
• In chemical reactions, mass remains consistent even though energy is absorbed or released.
• This concept is a cornerstone in nuclear physics where large energy transitions involve noticeable mass changes.

This relationship helps explain why in the given reaction of hydrogen and iodine, the mass of the products remains equal to the mass of the reactants despite energy changes.