Chapter 6: Chemistry of life

Which statement best describes isotopes of the same element?

• They have the same number of protons but different numbers of neutrons.

• They have different numbers of protons and the same number of neutrons.

• They have the same number of protons and neutrons but different numbers of electrons.

• They always have the same mass number.

Which statement best distinguishes a chemical change from a physical change when forming a compound?

• A chemical change creates a new substance with different properties, while a physical change does not create a new substance.

• Both chemical and physical changes create new substances with new properties.

• A physical change creates a compound, while a chemical change only changes the state of matter.

• Neither chemical nor physical changes alter the identity of the substances involved.

Which reagent is used in this MiniLab to test for the presence of simple sugars such as glucose, indicated by a color change?

• Biuret solution

• Benedict’s solution

• Iodine solution

• Silver nitrate

You prepare four test tubes with different food samples, add Benedict’s solution, and warm them in a 40–50°C water bath for 2–3 minutes. Which step best explains the purpose of warming the test tubes?

• It sterilizes the samples to prevent contamination.

• It accelerates the color-change reaction that indicates simple sugars.

• It evaporates water to concentrate the samples.

• It cools the solution to stop the reaction.

Which statement best describes van der Waals forces as presented in this section?

• They are strong bonds formed by sharing electrons equally between atoms.

• They are attractive forces between regions of slight positive and negative charge on nearby molecules.

• They are the forces that hold protons and neutrons together in the nucleus.

• They are the transfer of electrons from one atom to another creating ions.

What causes temporary areas of slight positive and negative charge that lead to van der Waals attractions?

• Electrons in a molecule remain fixed in place.

• Random motion of electrons can create an unequal distribution of the electron cloud.

• Protons move outside the nucleus creating charge imbalances.

• Neutrons convert into protons creating local charges.

Why can geckos climb smooth surfaces, according to the section?

• They produce glue-like secretions that harden on contact.

• They have claws that scratch microscopic grooves for grip.

• Van der Waals forces form between atoms in the hairlike structures on their toes and the surface.

• Their toes are magnetized and attract metal surfaces.

Which comparison about the strength of forces is accurate based on the text?

• Van der Waals forces are stronger than covalent bonds but weaker than ionic bonds.

• Van der Waals forces are as strong as covalent and ionic bonds.

• Van der Waals forces are not as strong as covalent and ionic bonds.

• Van der Waals forces occur only in water and therefore cannot be compared to bonds.

Which statement best describes activation energy in a chemical reaction?

• The total energy released when products form

• The minimum energy required to start the reaction

• The energy stored in the products only

• The difference between mass of reactants and products

In the context of enzymatic browning in apples, what role do enzymes play in chemical reactions?

• They increase the amount of product formed.

• They lower the activation energy and speed up reactions without being used up.

• They raise the activation energy to control the reaction rate.

• They permanently change into products during the reaction.