chemical reactions

Question 1

When does a chemical reaction occur?

Answer 1

A chemical reaction occurs when the atoms of one or more substances are rearranged to produce one or more different substances

Question 2

What is the result of a chemical reaction?

Answer 2

New substances with new properties will be formed

Question 3

What is a reactant

Answer 3

A starting material for a chemical reaction

Question 4

What is a product

Answer 4

A material produced from a chemical reaction

Question 5

What is the general representation of a chemical reaction (hint: it’s simpler than you think)

Answer 5

reactants -> products

Question 6

During chemical reactions, do reactions change directly into the products?

Answer 6

No, it takes time and energy for chemical bonds to be broken and made and the reactants are rearranged in multiple ways until they reach the final product.

Question 7

What is a reaction pathway

Answer 7

The path that atoms and molecules have to follow for the reactants to turn into products. Reactants have to progress along the reaction pathway, changing energy as it goes, until it reaches the final product.

Question 8

What changes as the reactants change and bonds are broken and remade?

Answer 8

The total energy of the reactants

Question 9

What is a reaction coordinate diagram?

Answer 9

A diagram that plots the energy of the reaction versus how much time has progressed

Question 10

When are atoms and molecules more stable?

Answer 10

When they have less energy

Question 11

When are atoms and molecules less stable?

Answer 11

When they have more energy

Question 12

What state (of energy) do chemical compounds try to move towards? Why?

Answer 12

A state of low energy, because it’s more stable

Question 13

What is ΔE? (definition)

Answer 13

The overall change in energy from the beginning to the end of a reaction.

Question 14

What is the formula for ΔE?

Answer 14

ΔE = (energy of products) - (energy of reactants)

Question 15

What is Ea? (definition)

Answer 15

The activation energy of a reaction, or the smallest amount of energy necessary to start a chemical reaction.

Question 16

Do all chemical reactions need Ea?

Answer 16

Yes. Activation energy is necessary to break the bonds of the reactants and form the bonds of the products. It is also necessary to start the reaction by overcoming the energy barrier.

Question 17

What is the formula for Ea?

Answer 17

Ea = (energy of transition states) - (energy of products)

Question 18

What is the transition state?

Answer 18

The state where the bonds of the reactants are breaking and the bonds of the products are forming. The highest in energy, used in order to get to the products.

Question 19

What is an exothermic reaction?

Answer 19

A reaction that produces energy, often heat, light or sound

Question 20

What is the formula of an exothermic reaction?

Answer 20

A+B=c+d+energy

Question 21

What is an endothermic reaction?

Answer 21

A reaction that needs energy to happen, so they take energy from their surroundings

Question 22

What is the formula of an endothermic reaction?

Answer 22

A+B+energy=C+d

Question 23

Are the products of an exothermic reaction more or less stable than the reactants?

Answer 23

More stable

Question 24

Are the products of an endothermic reaction more or less stable than the reactants?

Answer 24

Less stable

Question 25

When is ΔE positive or negative?

Answer 25

ΔE = (energy of products) - (energy of reactants)
Positive in endothermic reaction
Negative in exothermic reaction

Question 26

Is every reaction that requires some energy to start an endothermic reaction?

Answer 26

No. A reaction is exothermic if the amount of Ea is less than the amount of energy released, and a reaction is endothermic if the amount of energy released is less than the amount of Ea.

Question 27

What kind of reaction does a less stable allotrope go through to become a more stable allotrope?

Answer 27

Exothermic, because it needs to release energy to become more stable.

Question 28

What is a potential reason that a less stable allotrope might not react and become a more stable allotrope?

Answer 28

The reaction might have a high activation energy

Question 29

Do reactions occur at different rates?

Answer 29

Yes. Different reactions occur at different rates, and the same reaction might occur at a different rate depending on the conditions.

Question 30

What is chemical kinetics?

Answer 30

The field of science that studies the rates of chemical reactions. answers question “how fast will this occur?”

Question 31

What 3 things must happen for a reaction to occur?

Answer 31

1) particle of reactants must collide w/ each other
2) particles must possess enough activation energy/must be going a certain speed
3) must have the right “orientation”

Question 32

What is “collision theory”

Answer 32

Collision theory states that the frequency of particles colliding with each other successfully and reacting determines the reaction rate.

Question 33

How can the rate of a chemical reaction be increased? (3 and give explanations)

Answer 33

Concentration: more particles in a smaller space = more likely to collide
Temperature: more speed/moving faster = more likely to collide
Catalyst: Decreases the amount of energy necessary for the reaction to happen, makes it easier

Question 34

What is a catalyst?

Answer 34

• substance that changes the rate of a reaction
• same amount and identity post-reaction
• lowers the activation energy
• makes it so that it is more likely particles will have enough energy to react when they collide

Question 35

For the average reaction occurring at room temp, the raising the temp by 10 degrees celsius ___ the reaction rate.

Answer 35

Doubles the reaction rate