Chemical Reaction Exam Vocab Quiz

In a chemical equation, the substances present before the reaction takes place are called reactants. They are written on the left side of the arrow, which points towards the products. Reactants are the starting materials in a chemical reaction, and their interaction leads to the formation of new substances. For example, in the reaction between hydrogen and oxygen to form water, hydrogen and oxygen are the reactants.

In a decomposition reaction, a single compound breaks down into two or more simpler substances. This type of reaction is the opposite of a combination reaction, involving the splitting of a compound into its constituent elements or simpler compounds. For example, when water (H2O) undergoes electrolysis, it decomposes into hydrogen (H2) and oxygen (O2) gases. The general form of a decomposition reaction is AB → A + B.

A chemical change involves the rearrangement of atoms to form new substances with different properties. This process is fundamental to chemical reactions, distinguishing them from physical changes where no new substances are formed. Chemical changes are evidenced by indicators such as color change, gas production, and temperature change. For example, when iron rusts, it undergoes a chemical change to form iron oxide: 4Fe + 3O2 → 2Fe2O3.

Combustion reactions involve oxygen reacting with another substance, often producing carbon dioxide and water as products. This type of reaction is exothermic, releasing energy in the form of heat and light. Combustion is commonly associated with the burning of fuels such as hydrocarbons. For example, the combustion of methane (CH4) in the presence of oxygen (O2) produces carbon dioxide (CO2) and water (H2O): CH4 + 2O2 → CO2 + 2H2O.

Products are the substances formed as a result of a chemical reaction. They are written on the right side of the arrow in a chemical equation, indicating the new substances produced. For example, in the reaction between hydrogen and oxygen to form water, water is the product. The formation of products signifies the completion of the chemical change that started with the reactants.

A substance dissolved in water is called an aqueous solution, indicated by the symbol (aq) in a chemical equation. This notation shows that the substance is in a dissolved state in water, allowing for ionic and molecular interactions. For example, when sodium chloride (NaCl) dissolves in water, it forms an aqueous solution: NaCl(aq). The aqueous state is crucial for many chemical reactions, particularly those occurring in biological and environmental contexts.

In a double replacement reaction, two compounds react, and the positive and negative ions of the two reactants switch places, forming two new compounds. This type of reaction is common in precipitation and neutralization reactions. For example, when silver nitrate (AgNO3) reacts with sodium chloride (NaCl), silver chloride (AgCl) and sodium nitrate (NaNO3) are formed: AgNO3 + NaCl → AgCl + NaNO3. The general form of a double replacement reaction is AB + CD → AD + CB.

The Law of Conservation of Mass states that mass is neither created nor destroyed in a chemical reaction. This means the total mass of the reactants equals the total mass of the products. This principle is fundamental to balancing chemical equations and understanding the nature of chemical reactions.

A single replacement reaction occurs when one element replaces another element in a compound. This reaction involves an element reacting with a compound and displacing another element within that compound. For example, when zinc (Zn) reacts with hydrochloric acid (HCl), zinc replaces hydrogen, forming zinc chloride (ZnCl2) and hydrogen gas (H2): Zn + 2HCl → ZnCl2 + H2. The general form of a single replacement reaction is A + BC → AC + B.

An endothermic reaction absorbs heat from the surroundings, leading to a drop in temperature. These reactions require energy input to proceed and are characterized by a decrease in the temperature of the reaction mixture. An example of an endothermic reaction is the dissolving of ammonium nitrate (NH4NO3) in water, which absorbs heat and feels cold to the touch: NH4NO3 + H2O → NH4+ + NO3- + heat absorbed.

A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process. It works by lowering the activation energy needed for the reaction to proceed, thus speeding up the reaction. Catalysts are essential in many industrial and biological processes.

A neutralization reaction involves an acid and a base reacting to form water and a salt. This type of reaction is important in various chemical processes, including biological and industrial applications. An example of a neutralization reaction is the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) to form water (H2O) and sodium chloride (NaCl): HCl + NaOH → H2O + NaCl.

To balance a chemical equation, coefficients (whole numbers) are placed in front of the chemical formulas. This ensures that the number of atoms of each element is the same on both sides of the equation, following the law of conservation of mass. Balancing equations is essential to accurately represent the stoichiometry of a reaction. For example, the balanced equation for the combustion of methane is: CH4 + 2O2 → CO2 + 2H2O. Here, coefficients ensure that the same number of carbon, hydrogen, and oxygen atoms are present on both sides of the equation.

An exothermic reaction is one that releases heat to the surroundings. This type of reaction typically results in an increase in temperature of the environment. Exothermic reactions are common in everyday life, such as the burning of fuels and metabolic processes in living organisms. For example, the combustion of natural gas (methane) in a furnace releases heat, providing warmth: CH4 + 2O2 → CO2 + 2H2O + heat.

A combination reaction, also known as a synthesis reaction, occurs when two or more reactants combine to form a single, more complex product. This type of reaction is characterized by the merging of simpler substances to create a compound with new properties. An example of a combination reaction is the formation of water (H2O) from hydrogen (H2) and oxygen (O2) gases. The general form of a combination reaction is A + B → AB.