Check all the statements that are correct. Conservation of mass means:

1.Matter can be destroyed in a chemical reaction

2.We can start a reaction with different types of elements than we have at the end of the reaction.

3.We must start and end with the same amounts of matter

4.Matter cannot be created


Question 2

Select all of the signs of a chemical reaction

1.A solid is formed

2.The change can be easily undone

3.The state of matter changes

4.A gas is released

5.A temperature change happens

6.A color change happens


Question 3

A chemical reaction.........

1.Creates one or more new substances

2.Happens in the water cycle

3.Is only a physical change

4.Is when something changes the state of matter


Question 4

Changing from one state of matter to another is a

1.Physical change

2.Chemical reaction

3.Chemical change

4.Optical illusion


Question 5

During a chemical reaction.......

1.The substances change by rearranging the atoms and elements

2.Matter can be destroyed

3.New matter is created

4.Energy is created

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Best Answer


Question 1: Correct 3 and 4

Question 2: All can be corrected except item 2.

Question 3: Correct 1

Question 4: Correct 1

Question 5: Correct 1


Question 1: The law of conservation of mass explains that “In an isolated system, during any ordinary chemical reaction, the total mass in the system remains constant, that is, the mass consumed of the reagents is equal to the mass of the products obtained”, therefore, statements 3 are correct, which tells us that we must begin and end with the same amount of matter, and 4, since we cannot create or destroy matter.

Question 2: When a chemical reaction occurs, according to the initial compounds (reagents), it can be seen in various ways how a change in the system occurs, which indicates that a chemical reaction occurred, many of them can be identify with our senses (change of color, change of temperature, change of state of aggregation of the reagents, etc.), it is clear that they do not have problems that have all these statements together, with which of these happen, we could affirm that it had a chemical reaction.

On the other hand, changes that can be easily undone (affirmation 2) are more related to physical phenomena, in which the intimate composition of matter (such as a change of state) does not vary, a difference in chemical reactions .

Question 3: When a chemical reaction occurs, the substances that are initially found (reagents) change the intimate structure of matter, breaking and / or forming bonds of the compounds to form new bonds, and thus, new substances (products). That is why the correct statement is 1, in the case of the other statements, physical phenomena are being described, in which there are no breaking of bonds in the initial compounds to form new substances, simply, state changes occur in matter, but no new compounds are formed.

Question 4: In changes of state, there are no changes in the intimate structure of matter, so they are physical phenomena. The only thing that varies in the changes of state of matter, is the kinetic energy with which the particles of the system move, due to the variation in temperature.

Question 5: Unlike physical reactions, in chemical reactions there are bond ruptures and / or rearrangement of atoms of the initial compounds (reagents) to form new bonds and structures, and thus, new compounds (reaction products). In addition, these reactions comply with the law of conservation of mass, so that matter cannot be created or destroyed, as well as energy.

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