Which Is characteristic of all mixtures? (1) They are homogeneous. (2) They are heterogeneous. (3) Their compositions are in a definite ratio. (4) Their compositions may vary.

A compound differs from a mixture In that a compound always has a (1) homogeneous composition, (2) maximum of two elements, (3) minimum of three elements, (4) heterogeneous composition.

Which of the following cannot be decomposed by chemical means? (1) sodium, (2) ethanol, (3) sucrose, (4) water.

Most elements are (1) metals, (2) nonmetals, (3) gases, (4) made in a laboratory.

A compound differs from an element in that a compound (1) is homogeneous, (2) has a definite composition, (3) has a definite melting point, (4) can be decomposed by a chemical reaction.

Which statement is an identifying characteristic of a mixture? (1) A mixture can consist of a single element. (2) A mixture can be separated by physical means. (3) A mixture must have a definite composition by weight. (4) A mixture must be homogeneous.

Which substance takes the shape of and fills the volume of any container into which it is placed? (1) $\mathrm{H}_{2} \mathrm{O}(\ell)$ (2) $\mathrm{CO}_{2}(g)$ (3) $I_{2}(s)$ (4) $\mathrm{Hg}(\ell)$

Each particle contained in hydrogen gas is made up of two identical hydrogen atoms chemically joined together. Hydrogen gas is (1) a compound, (2) an element, (3) a homogeneous mixture, (4) a heterogeneous mixture.

Which substance can be decomposed by a chemical change? (1) ammonia, (2) aluminum, (3) magnesium, (4) manganese.

What Is the total mass of Rn-222 remaining in an original 160-mg sample of Rn-222 after 19.1 days? (1) 2.5 mg, (2) 5.0 mg, (3) 10 mg, (4) 20 mg.

Which must be a mixture of substances? (1) solid, (2) liquid, (3) gas, (4) solution.

In a chemical equation, how do you show that catalysts are not consumed or chemically altered during a reaction?

Write a chemical equation showing reactants, products, and catalysts needed (if any) for the reaction of propene with each of the reactants in Problem 13.70. Use Markovnikov’s rule as needed.

Certain proteins, known as enzymes, serve as catalysts for chemical reactions in living things. In 1913 Leonor Michaelis and L. M. Menten discovered the following formula giving the initial speed V (in moles per liter per second) at which the reaction begins in terms of the amount of substrate x (the substance being acted upon, measured in moles per liters) present: $V=\frac{a x}{x+b}$ where a and b are positive constants. Evaluate $\lim _{x \rightarrow \infty} \frac{a x}{x+b}$ and interpret your result.