Chemical changes in matter.

When there is a release of gas it always means that

a chemical change is taking place.

• TRUE

• FALSE

In a considerable number of chemical reactions no new

substances appear.

• TRUE

• FALSE

The vaporization of water is a chemical change, because a

new substance appears.

• TRUE

• FALSE

Complete the sentence with the correct option: «When a chemical reaction takes place a new substance appears because…

• … new atoms are created.»

• … the atoms of the substances that react are re-ordered.»

• … the atoms of the substances that react disappear.»

• … it comes from a change of state.»

Indicate what the reactants are in this chemical reaction:

Aluminium is combined with hydrochloric acid and aluminum trichloride and hydrogen is released.

• Aluminium + hydrochloric acid

• Aluminum trichloride + hydrogen

• None of the above

Indicate what the products are in this chemical reaction:

Aluminium is combined with hydrochloric acid and aluminum trichloride and hydrogen is released.

• Aluminium + hydrochloric acid

• Aluminum trichloride + hydrogen

• None of the above

Indicate which chemical equation corresponds to this reaction: Magnesium (Mg) is combined with hydrochloric acid (HCl) and magnesium dichloride is formed (MgCl₂) and hydrogen (H₂) is released.

• Mg + HCl -----> MgCl₂ + H₂

• Mg + 2 HCl -----> MgCl₂ + H₂

• Mg + HCl -----> MgCl + H

• Mg + 2 HCl -----> MgCl₂ + H₂

Solve the following exercise using the law of conservation of matter: 36.5 g of hydrochloric acid (HCl) reacts with 40 g of sodium hydroxide (NaOH) resulting in 58.5 g of sodium chloride (NaCl) causing a certain amount of water (H₂O) to be formed. Choose the option that represents the amount of water formed:

• 55 g of water.

• 18 g of water.

• 18 litros of water.

• 47 g of water.

Solve the following exercise using the law of conservation of matter: When 6 g of hydrogen reacts with 30 g of nitrogen, there are 2 g of nitrogen left over that do not react. Knowing that ammonia is the only product of the reaction, what mass is obtained?

• 36 g

• 24 g

• 34 g

• 32 g

Out of the following factors, which ones influence the speed of a chemical reaction?:

• The mass of the reactants & the density of the reactants.

• The temperature & the concentration of the reactants.