HESI A2 Version 1 Chemistry

Correct Answer: D

Rationale: A combustion reaction is a type of chemical reaction that involves a substance reacting with oxygen gas to produce heat and light. This reaction is exothermic, releasing energy in the form of heat and light. The correct answer is D because combustion reactions specifically involve oxygen as a reactant, leading to the production of heat and light as byproducts.

Correct Answer: C

Rationale: The correct answer is C: Average mass of that element's isotopes. Atomic mass is the weighted average mass of the isotopes of an element, considering the natural abundance of each isotope. It is not just the sum of protons and neutrons or neutrons and electrons. Understanding atomic mass is crucial in chemistry as it helps in determining the molar mass of elements, which is essential in various chemical calculations such as stoichiometry and reaction equations.

Correct Answer: D

Rationale: A combustion reaction is a chemical process that involves a substance reacting with oxygen to produce heat and light. The key component in a combustion reaction is oxygen, making choice D the correct answer. Combustion reactions are typically exothermic, releasing energy in the form of heat and light, making choice A incorrect. Choices B and C describe different types of chemical reactions, not combustion reactions. Therefore, the correct answer is D.

Correct Answer: B

Rationale: The reaction KCl → K + Cl2 is an example of a decomposition reaction. In a decomposition reaction, a compound breaks down into its constituent elements or simpler compounds. In this case, potassium chloride (KCl) decomposes into potassium (K) and chlorine gas (Cl2). Therefore, the correct answer is B, Decomposition.