Physical Science --- Chapter 6

The correct answer is sodium chloride because when sodium reacts with chlorine gas, they undergo a synthesis reaction forming sodium chloride. This reaction occurs due to the transfer of electrons from sodium to chlorine, resulting in the formation of ionic bonds between sodium cations and chloride anions, creating the compound sodium chloride.

When a metal rusts, it undergoes a chemical reaction with oxygen in the presence of moisture. This reaction results in the formation of a new compound, iron oxide, which gives the metal a reddish-brown color. Since rusting involves a chemical reaction and the formation of a new substance, it is considered a chemical change rather than a physical change. Therefore, the change in color, such as rusting of metal, serves as a sign that a chemical change is taking place.

In a chemical reaction, atoms are rearranged. This means that the bonds between atoms are broken and new bonds are formed, resulting in the formation of different molecules or compounds. The number of atoms remains the same before and after the reaction, but their arrangement changes, leading to the formation of new substances with different properties.

In a synthesis reaction, two or more compounds combine to form a new, more complex compound. This is the opposite of a decomposition reaction, where a compound is broken down into simpler substances. In a synthesis reaction, the reactants come together to create a product that is more complex and has a higher molecular weight. This can involve the rearrangement of atoms or the formation of new bonds. The formation of a new compound is the defining characteristic of a synthesis reaction.

In a chemical reaction, substances undergo a change as they react with each other to form new substances. These substances that participate in the reaction and are consumed or used up in the process are called reactants. Therefore, the correct answer is "a reactant."

A smaller surface area does not speed up a chemical reaction because it limits the contact between reactant molecules, reducing the chances of successful collisions. Higher pressure, higher temperature, and the presence of a catalyst all increase the rate of reaction by increasing the frequency of collisions and/or lowering the activation energy required for the reaction to occur.

In a balanced chemical reaction, the law of conservation of mass states that the total mass of the reactants must be equal to the total mass of the products. This means that no atoms are created or destroyed during a chemical reaction, only rearranged. Therefore, the correct answer is that the total mass of the reactants always equals the total mass of the products.

Endothermic reactions are characterized by the absorption of energy from the surroundings. This means that energy is transferred from the surroundings to the reactants, resulting in an increase in the energy of the reactants. This energy can be in the form of heat, but it can also be in other forms such as light or electrical energy. Therefore, the statement "Energy is transferred from the surroundings to the reactants" is correct for endothermic reactions.

In an exothermic reaction, energy is released from the reactants to the surroundings. This means that the reactants have a higher energy level than the surroundings, and as the reaction occurs, the energy is transferred to the surroundings, resulting in an increase in temperature. This is why exothermic reactions are often associated with the release of heat or light.

When water is broken down by electrolysis, it undergoes a chemical reaction that separates it into its component elements. Electrolysis involves passing an electric current through water, causing it to decompose. During this process, hydrogen gas is produced at the cathode (negative electrode) and oxygen gas is produced at the anode (positive electrode). Therefore, the correct answer is hydrogen gas and oxygen gas.