A. Hydrogen peroxide decomposes to form water and oxygen. Manganese dioxide is used in the reaction to increase the rate of the reaction and remains unchanged by the end of the reaction. What are the reactant(s), catalyst, and product(s), respectively, for the decomposition reaction of hydrogen peroxide? B. A large amount of heat energy was supplied during a combustion reaction. Which of the following symbols should be used in the chemical equation to represent the heat supplied during the reaction? C. The skeleton chemical equation for the reaction between zinc metal and hydrochloric acid is shown. Zn + HCl ? ZnCl 2 + H 2 what should be done to balance the equation? Therapeutic cold packs are particularly beneficial for relieving pain due to athletic and sports injuries. The cold packs developed initially contained toxic chemicals. To make these packs more suitable for use by the general public, a researcher developed a cold pack composed of nontoxic chemicals such as urea, sodium acetate, potassium chloride, ammonium chloride, and guar gum. When a reaction was triggered between these chemical substances, temperatures as low as -7°C were achieved and were reportedly maintained for a minimum of 30 minutes.
The Correct Answer and Explanation is :
A. Decomposition of Hydrogen Peroxide Reaction:
- Reactant(s): Hydrogen peroxide (H₂O₂)
- Catalyst: Manganese dioxide (MnO₂)
- Product(s): Water (H₂O) and oxygen (O₂)
The decomposition of hydrogen peroxide occurs in the presence of manganese dioxide, which acts as a catalyst. A catalyst increases the rate of a reaction without being consumed in the reaction itself. Hydrogen peroxide (H₂O₂) breaks down into water (H₂O) and oxygen (O₂). Manganese dioxide speeds up the process, but it does not undergo any permanent change during the reaction, so it remains unchanged by the end of the reaction.
The chemical equation for this reaction is:
[
2H_2O_2 \xrightarrow{MnO_2} 2H_2O + O_2
]
B. Symbol for Heat Energy in Combustion Reactions:
In a combustion reaction, heat energy is released when a substance reacts with oxygen. To represent heat being supplied during the reaction in a chemical equation, the symbol used is usually Δ (delta), which indicates that heat is being either absorbed or released during the process. If heat is supplied, it is typically written as Δ or the heat source is noted as being on the product side.
For example:
[
C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O + \Delta
]
The Δ indicates that heat is released during the combustion of propane.
C. Balancing the Reaction Between Zinc and Hydrochloric Acid:
The skeleton equation for the reaction between zinc metal (Zn) and hydrochloric acid (HCl) is:
[
Zn + HCl \rightarrow ZnCl_2 + H_2
]
To balance the equation, start by balancing the atoms on both sides:
- There is 1 zinc (Zn) atom on both sides.
- There are 2 chlorine (Cl) atoms on the right side (in ZnCl₂), so you need 2 HCl molecules on the left side.
- To balance hydrogen (H), there will be 2 hydrogen atoms on the left side, so 1 molecule of H₂ is needed on the right.
The balanced equation is:
[
Zn + 2HCl \rightarrow ZnCl_2 + H_2
]
This equation shows that 1 molecule of zinc reacts with 2 molecules of hydrochloric acid to produce 1 molecule of zinc chloride (ZnCl₂) and 1 molecule of hydrogen gas (H₂).
Explanation of the Cold Pack Reaction:
Therapeutic cold packs are designed to cool down and relieve pain caused by sports injuries. These cold packs use an endothermic reaction, where heat is absorbed from the surroundings, lowering the temperature. The reaction between substances like urea, sodium acetate, potassium chloride, ammonium chloride, and guar gum is triggered when the pack is activated (usually by breaking a barrier inside the pack). These substances react with each other in a way that absorbs energy, causing the temperature to drop significantly, reaching as low as -7°C and maintaining this temperature for a period.
This endothermic reaction is beneficial because it provides sustained cooling without the need for external refrigeration, and the chemicals used (like ammonium chloride and sodium acetate) are non-toxic, making the pack safe for general public use. The guar gum acts as a stabilizer, helping to maintain the integrity of the pack and ensuring the chemical reaction occurs evenly. This type of cold pack is particularly useful for treating injuries like sprains, strains, and swelling, as it can be easily applied to reduce inflammation and numb pain.