Chapter 7 Test: Chemical Equations

1. The products and the reactants in the reaction have the same ___.

Atoms

Molecules

Subscripts

Bond energies

In a chemical reaction, the atoms present in the reactants rearrange to form the products. The number and type of atoms in the reactants must be equal to the number and type of atoms in the products, according to the law of conservation of mass. Therefore, the correct answer is "atoms" as both the reactants and products have the same number of atoms.

Explanation

In a chemical reaction, the atoms present in the reactants rearrange to form the products. The number and type of atoms in the reactants must be equal to the number and type of atoms in the products, according to the law of conservation of mass. Therefore, the correct answer is "atoms" as both the reactants and products have the same number of atoms.

2. A chemical reaction has not occurred if the products have ___.

The same mass as the reactants

Less total bond energy than the reactants

More total bond energy than the reactants

The same chemical properties as the reactants

If the products of a chemical reaction have the same chemical properties as the reactants, it indicates that no new substances with different properties have been formed. This suggests that no chemical reaction has occurred.

Explanation

If the products of a chemical reaction have the same chemical properties as the reactants, it indicates that no new substances with different properties have been formed. This suggests that no chemical reaction has occurred.

3. C(s) + O2(g) → CO2(g)+ energy is a chemical reaction because ____.

It releases energy

The chemical properties of CO2 are different from the individual properties of carbon and oxygen

It absorbs energy

CO2 is a gas and carbon is a crystal

This answer is correct because a chemical reaction involves the rearrangement of atoms to form new substances with different chemical properties. In this reaction, carbon and oxygen combine to form carbon dioxide, which has different properties compared to the individual elements.

Explanation

This answer is correct because a chemical reaction involves the rearrangement of atoms to form new substances with different chemical properties. In this reaction, carbon and oxygen combine to form carbon dioxide, which has different properties compared to the individual elements.

4. A balanced equation represents the law of mass conservation, and as a result all of the following are true except ___.

The number of moles of products equals the number of moles of reactants

The total mass of the product equals the total mass of the reactants

The number of atoms in the products equals the number of atoms in the reactants

The states of matter of the products are independent of the states of reactants

The balanced equation represents the law of mass conservation, which means that the total mass of the products is equal to the total mass of the reactants. It also ensures that the number of atoms in the products is equal to the number of atoms in the reactants. Additionally, the states of matter of the products can be different from the states of matter of the reactants. However, the number of moles of products does not necessarily have to be equal to the number of moles of reactants.

Explanation

The balanced equation represents the law of mass conservation, which means that the total mass of the products is equal to the total mass of the reactants. It also ensures that the number of atoms in the products is equal to the number of atoms in the reactants. Additionally, the states of matter of the products can be different from the states of matter of the reactants. However, the number of moles of products does not necessarily have to be equal to the number of moles of reactants.

5. The chemical reaction is exothermic if ___.

∆H is a negative value

∆H is a positive value

Energy is absorbed during the reaction

Energy is conserved during reaction

An exothermic reaction is characterized by the release of energy in the form of heat. When the enthalpy change (∆H) is negative, it indicates that the reactants have a higher energy level than the products. This means that energy is being released during the reaction, making it exothermic.

Explanation

An exothermic reaction is characterized by the release of energy in the form of heat. When the enthalpy change (∆H) is negative, it indicates that the reactants have a higher energy level than the products. This means that energy is being released during the reaction, making it exothermic.

6. The only single-displacement reaction among the following chemical equations is ___.

2H2O2(l) → 2H2O(l) + O2(g)

Pb(s) + Hg2SO4(s) → PbSO4(s) + 2Hg(l)

2NH3(g) → N2(g) + 3H2(g)

NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO→3(aq)

The given equation 2H2O2(l) → 2H2O(l) + O2(g) is the only single-displacement reaction among the options. In this reaction, hydrogen peroxide (H2O2) decomposes to form water (H2O) and oxygen gas (O2). A single-displacement reaction involves the replacement of one element in a compound by another element. In this case, the oxygen atoms in H2O2 are being displaced by the formation of O2 gas. The other equations do not involve the displacement of one element by another, making them different types of reactions.

Explanation

The given equation 2H2O2(l) → 2H2O(l) + O2(g) is the only single-displacement reaction among the options. In this reaction, hydrogen peroxide (H2O2) decomposes to form water (H2O) and oxygen gas (O2). A single-displacement reaction involves the replacement of one element in a compound by another element. In this case, the oxygen atoms in H2O2 are being displaced by the formation of O2 gas. The other equations do not involve the displacement of one element by another, making them different types of reactions.