Unit 7 - Chemical Reactions Review

Rust forming on a car body is a chemical reaction because it involves a chemical change. Rust is formed when iron reacts with oxygen in the presence of water or moisture, resulting in the formation of iron oxide. This process is known as oxidation and is a chemical reaction. In contrast, the other options mentioned are physical changes rather than chemical reactions.

When iron combines with oxygen and water in the air to form rust, the substance that is produced in the reaction is rust. Rust is a reddish-brown compound that forms on the surface of iron when it reacts with oxygen and water. It is a common form of corrosion and is composed mainly of hydrated iron(III) oxide.

A chemical equation is a way to describe a chemical reaction using chemical formulas and symbols. It represents the reactants and products involved in the reaction and provides information about the stoichiometry of the reaction, such as the number of molecules or moles of each substance. It allows scientists to understand and communicate the specific chemical changes that occur during a reaction. The other options, synthesis, a physical law, and the law of conservation of matter, do not accurately describe the concept of using chemical formulas and symbols to represent a chemical reaction.

Coefficients in chemical equations represent the number of units of each substance. They are used to balance the equation by ensuring that the number of atoms on both sides of the equation is equal. Coefficients indicate the ratio in which substances react or are produced in a chemical reaction.

The correct answer is "always equals the mass of the reactants." This is based on the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the products must be equal to the total mass of the reactants.

A catalyst is a substance that speeds up a chemical reaction without being permanently changed itself. It works by lowering the activation energy required for the reaction to occur, allowing it to happen more quickly. This is achieved by providing an alternative reaction pathway with a lower energy barrier. The catalyst is not consumed in the reaction and can be used repeatedly.

In a chemical reaction, new substances are formed as a result of the reaction. These new substances are called products. Reactants are the substances that undergo the reaction, while coefficients are used to balance the equation representing the reaction. Resultants is not a term commonly used in chemistry to describe the new substances formed in a chemical reaction.

A change in which one or more substances are converted into new substances is known as a chemical reaction. In a chemical reaction, the bonds between atoms in the reactants are broken and new bonds are formed to create different substances. This process involves the rearrangement of atoms and the release or absorption of energy. Unlike physical changes, which only affect the physical properties of a substance, chemical reactions result in the formation of entirely new substances with different chemical properties.

The law of conservation of mass states that matter is not created or destroyed, but is conserved. This means that in a chemical reaction, the total mass of the reactants will be equal to the total mass of the products. The atoms in the reactants may rearrange to form different molecules in the products, but the total number of atoms remains the same. This principle is fundamental in chemistry and is used to balance chemical equations and analyze reactions.

Diatomic molecules refer to combinations of two atoms that are usually found together. These molecules can be made up of the same element or different elements. Examples of diatomic molecules include oxygen (O2), nitrogen (N2), and hydrogen (H2). These molecules are stable and have specific properties that differ from their individual atoms.

A balanced chemical equation means that the number of atoms of each element is the same on both sides of the equation. This is important because it ensures that the law of conservation of mass is obeyed. In a balanced equation, the total mass of the reactants is equal to the total mass of the products, indicating that no atoms are created or destroyed during the reaction. By adjusting the coefficients in the equation, we can achieve this balance and accurately represent the reaction.

When the temperature of the beaker holding the reacting substances is decreased, it indicates that heat is being absorbed from the surroundings. This suggests that the reaction is endothermic, as it requires an input of energy (in the form of heat) to proceed.

The formation of frost on the outside of the beaker suggests that heat is being absorbed from the surroundings, causing a decrease in temperature. This indicates an endothermic reaction, as it requires an input of energy in the form of heat to occur.

In a synthesis reaction, two or more substances combine to form another substance. This type of reaction is characterized by the formation of a new compound from simpler reactants. It involves the combination of atoms or molecules to create a more complex product.

During a double displacement reaction, two compounds exchange ions to form two new compounds. Sometimes, one of the products formed is insoluble in the reaction mixture and separates out as a solid. This solid is called a precipitate. Therefore, the correct answer is precipitate.

When an electric current passes through water, a process known as electrolysis occurs. During electrolysis, water molecules are broken down into their constituent elements. The positive electrode (anode) attracts negatively charged hydroxide ions (OH-) and causes the oxidation of water molecules, resulting in the release of oxygen gas (O2). At the same time, the negative electrode (cathode) attracts positively charged hydrogen ions (H+) and causes the reduction of water molecules, leading to the formation of hydrogen gas (H2). Therefore, the expected products of the decomposition reaction are hydrogen and oxygen.

When the temperature of the beaker holding the reacting substances is increased, it indicates that heat is being released from the reaction. This release of heat is characteristic of an exothermic reaction, where energy is transferred from the system (reacting substances) to the surroundings (beaker). Therefore, the correct answer is exothermic.

The chemical formula for a compound tells what elements it contains. The chemical formula represents the types and number of atoms of each element present in the compound. It provides a concise and standardized way to represent the composition of a compound. By knowing the chemical formula, one can determine the elements that make up the compound and their respective ratios.

Double displacement reactions produce a precipitate. In a double displacement reaction, the positive ions of two compounds switch places, forming two new compounds. If one of the products is insoluble in water, it will form a solid precipitate. This occurs because the positive and negative ions of the reactants combine to form an insoluble compound, which then separates from the solution as a solid.

Oxygen is written with a subscript 2 because it usually exists as a diatomic molecule. This means that oxygen atoms typically bond together in pairs, forming O2 molecules. This is the most stable and common form of oxygen found in nature.