Which of the following can only be separated into two or more pure substances by a chemical change?

a. an element

b. a compound

c. a homogeneous mixture

d. a heterogeneous mixture

Which of the following best explains why the atomic theory changed over the past 200 years? The theory was terribly flawed. Few people believed it was correct. The atomic model was incomplete. New experiments led to revised ideas.

Small differences between parents and offspring accumulate over time. This process A. prevents parents from being able to care for their offspring. B. results in only one type of organism that has the exact same characteristics as its ancestors. C.

Nitrogen gas and hydrogen gas react to form ammonia according to the following thermochemical equation. 3H2+N2⟶2NH3ΔH=-96kJ Write the balanced chemical equation for a reaction involving these substances with the following change in enthalpy.

Why do metals lose shine but gold does not?

Which one of the following substances is a liquid fuel used in rocket engines? a. Liquid oxygen b. Amnonia c. Condium nitrate d. Potassium

Determine the molecular formula for the unknown if the molecular mass is 60.0 amu and the empirical formula is ch2o.

Draw the organic product of the following nucleophilic reaction

How does the energy of the activated complex compare with the energies of reactants and products? select one: a. it is lower than the energy of both reactants and products. b.

A student asked to convert measurements from liters to mililiters and from mililiters to liters. His answers are shown in bold in the choices shown below. On which choice did he make a mistake?

Donald is making a model of a nitrogen atom. The box for nitrogen in the periodic table is shown. To represent a neutral atom, which of these must Donald include in his model?