Chemical reactions

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.

Which observation does NOT indicate that a chemical reaction has occurred?

• formation of a precipitate

• evolution of heat and light

• change in total mass of substances

• production of a gas

A solid produced by a chemical reaction in solution that separates from the solution is called

• a precipitate

• a molecule

• a reactant

• the mass of the product

After the correct formula for a reactant in an equation has been written, the

• subscripts are adjusted to balance the equation.

• formula should not be changed.

• same formula must appear as the product.

• symbols in the formula must not appear on the product side of the equation.

In writing an equation that produces hydrogen gas, the correct representation of hydrogen gas is

• H

• 2H

• H2

• OH

What is the small whole number that appears in front of a formula in a chemical equation?

• a subscript

• a ratio

• a superscript

• a coefficient

To balance a chemical equation, it may be necessary to adjust the

• coefficients.

• formulas of the products.

• subscripts

• number of products.

According to the law of conservation of mass, the total mass of the reacting substances is

• always more than the total mass of the products.

• always less than the total mass of the products.

• sometimes more and sometimes less than the total mass of the products.

• always equal to the total mass of the products.

A chemical equation is balanced when the

• coefficients of the reactants equal the coefficients of the products.

• same number of each kind of atom appears in the reactants and in the products.

• products and reactants are the same chemicals.

• subscripts of the reactants equal the subscripts of the products.

Which word equation represents the reaction that produces water from hydrogen and oxygen?

• Water is produced from hydrogen and oxygen.

• Hydrogen plus oxygen yields water.

• H2 + O2 --> water.

• Water can be separated into hydrogen and oxygen.