Chemical Reaction

Which of the following may signal that a new substance has formed? Select one: A solid forms when two liquids are mixed All of these are correct. A change in color Bubbles form

All of these are correct.

Select the true statement: Bonds are broken and new bonds are formed during physical changes only. Bonds are broken and new bonds are formed during chemical reactions only. Bonds do not change in either chemical reactions or physical changes.

Bonds are broken and new bonds are formed during chemical reactions only.

Identify the product(s) in the following chemical reaction: C r 2 O 3 + 3 C → 2 C r + 3 C O Select One: Chromium and carbon monoxide Chromium(III) oxide and carbon Chromium and carbon dioxide

Chromium and carbon monoxide

Mixing hydrochloric acid and sodium hydroxide is an example of an exothermic reaction. This means: Energy is taken in during the chemical reaction. Energy is released during the chemical reaction. There is no change in energy during the chemical reaction

Energy is released during the chemical reaction.

Identify the reactant(s) of the following chemical reaction: 4 A g + 2 H 2 S + O 2 → 2 A g 2 S + 2 H 2 O Select One: Silver and oxygen Silver sulfide and water Silver, oxygen and hydrogen sulfide

Silver, oxygen and hydrogen sulfide

Which statement about energy and chemical reactions is true? Select One: Some chemical reactions absorb and some release energy. All chemical reactions release energy. All chemical reactions absorb energy.

Some chemical reactions absorb and some release energy.

Which of the following describes the Law of Conservation of Mass? The products will have the same states of matter as the reactants. The mass of the reactants is greater than the mass of the products. The mass of the products equals the mass of the reactants.

The mass of the products equals the mass of the reactants.

In a chemical reaction, which of the following is true of the products? Select One: The products retain the same physical properties as the reactants. The products retain the same shape as the reactants. The products retain the same number atoms as the reactants.

The products retain the same number atoms as the reactants.

In a chemical equation, what does the symbol "⇄" mean? Select One: The reaction needs a catalyst in order to complete. The reaction is reversible and can go in both directions. The reaction is at equilibrium.

The reaction is reversible and can go in both directions.

Why are numbers placed before the elements and molecules in a chemical equation? Select One: To balance the equation so that it has the same number of atoms of each element on each side. To represent if an element or molecule is a liquid, gas, or solid To show whether a substance is an element or molecule

To balance the equation so that it has the same number of atoms of each element on each side.

Liquid water (H2O) is formed when two gases, hydrogen (H2) and oxygen (O2), react. Why are the properties of water different than the reactant gases? Select One: When substances chemically combine, products with completely different properties form. The difference in the properties of water can be attributed to physical changes to the hydrogen and oxygen atoms on a subatomic level. The properties of the gases are combined to give water its properties.

When substances chemically combine, products with completely different properties form.

The element sodium (Na) is a soft solid that will react explosively with water. The element chlorine (Cl) is a toxic gas. When these two elements combine, they produce a stable, crystalline solid known commonly as table salt (NaCl). How would you explain this? Select One: Sodium and chlorine become different elements during the reaction. When substances combine to form new substances, the properties of the resulting substances will be different than those of the reactants. When substances combine to form new substances, the properties of the reactants are preserved.

When substances combine to form new substances, the properties of the resulting substances will be different than those of the reactants.

Complete the following sentence: "During a chemical reaction:" Select One: the number of atoms in the product(s) is less than those of the reactant(s). a new substance(s) with the same number of atoms as the initial substance(s) is formed. the mass of the atoms of the product(s) is greater than those of the reactant(s).

a new substance(s) with the same number of atoms as the initial substance(s) is formed.

An athlete injures her knee and requests a cold pack. Her coach finds a cold pack at room temperature in the First Aid kit. To activate the cold pack, the coach squeezes it several times. After 30 seconds, the cold pack then becomes cold. What kind of reaction is happening inside the cold pack? Selec One: elastic evaporative endothermic

endothermic

Cold packs are used on injuries to reduce swelling and pain. The cold pack contains ammonium nitrate and water with a barrier between the two compounds. When used, the barrier is broken by squeezing the pack, it becomes cold. What type of reaction is this? Select One: endothermic exothermic enthalpic

endothermic