Energy Changes and Rates of Reaction

Question 1

Whenever a chemical reaction happens, the total amount of energy stored in the bonds of the reactants is different from the total amount of energy stored in the bonds of the products. That means that the total energy has changed: energy has either been __________ or __________.

Answer 1

Released or consumed.

Question 2

The correct unit for energy is _________.

Answer 2

joules.

Question 3

________________ ___________ is the minimum energy required before a reaction can occur.

Answer 3

Activation energy

Question 4

Typically, chemical reactions that have low activation energies are considered more volatile and ______ likely to happen. Reactions that have high activation energies are ______ likely to occur because it takes great energy to start the reaction.

In addition, reactions that have high activation energy tend to occur at a _________ rate.

Answer 4

low = more likely
high = less likely
= slower rate.

Question 5

_________ is the capacity to do work or to produce heat.

Answer 5

Energy

Question 6

__________ states that energy can be converted from one form to another but can be neither created nor destroyed - energy in the universe is constant.

Answer 6

The Law of Conservation of Energy

Question 7

Energy can be classified as either

Answer 7

potential or kinetic.

Question 8

Work is defined as

Answer 8

force acting over distance.

Question 9

Chemists represent the pathways molecules follow as they collide to form products with a _________________. These diagrams display how potential energy changes from reactants to products over the course of the reaction.

Answer 9

potential energy diagram

Question 10

At the peak of the energy is the __________. An ____________ is a group of unstable intermediary substances that form at the moment of the collision.

Answer 10

activated complex

Question 11

The amount of energy needed from the reactant to form the activated complex is the

Answer 11

activation energy.

Question 12

The amount of energy change between the reactants and products is called the __________. Depending on the reaction, the heat of the reaction can be a positive value or a negative value.

Answer 12

heat (or enthalpy) of the reaction

Question 13

_____________ of a substance is the amount of heat energy required to raise the temperature of one gram of the substance by one Celsius degree or one Kelvin.

Answer 13

The heat capacity

In other words, the specific heat capacity of a substance is heat capacity per gram.

Question 14

_________ is the science of measuring heat based upon temperature changes as an object absorbs or loses heat energy.

Answer 14

Calorimetry

Question 15

All combustion reactions release heat energy to the surroundings and are subsequently referred to as ___________ reactions.

Answer 15

exothermic

Question 16

The _______________ of a substance is the amount of heat absorbed or given off when 1 mole of the substance is formed at STP from its elements in their standard states.

Answer 16

standard enthalpy of formation

Question 17

________ states that the enthalpy change for any reaction depends only on the reactants and products and is independent of the path of the reaction or the number of steps taken to the product(s).

Answer 17

Hess’s Law

Question 18

A ___________ is a series of small reaction steps that involve a few reactant particles.

Answer 18

A reaction mechanism

Question 19

______________ are particles that form during the reaction mechanism that are not the initial reactants or the final products. They help explain how the reaction takes place by showing how various bonds are broken and formed.

Answer 19

Intermediates

Question 20

One step in a reaction mechanism is always slower than the rest. This is called the ___________ which has higher activation energy, so it takes longer than the other steps do. This step determines the overall reaction rate.

Answer 20

rate determining step

Question 21

A ____________ has a rate which is independent of the concentration of the reactant(s). Increasing the concentration of the reacting species will not speed up the rate of the reaction.

Answer 21

zero order reaction

Question 22

A _____________ depends on the concentration of only one reactant. For example, if the concentration of that particular reactant is doubled, the rate doubles as well.

Answer 22

first-order reaction

Question 23

A ___________ depends on the concentrations of one second-order reactant, or two first-order reactants. For example, if the concentration of that particular reactant is doubled, the reaction rate increases fourfold.

Answer 23

second-order reaction

Question 24

Atoms that have different number of neutrons are called __________.

Answer 24

isotopes

Question 25

The nucleus composes over 99.9% of the mass of the entire atom. The nucleus is held together by the _________, but is effective only when the subatomic particles are close together.

Answer 25

nuclear force

Question 26

________ is a nuclear process in which two light nuclei combine to form a single, heavier nucleus.

Answer 26

Fusion

Question 27

_________ is a nuclear process in which a heavy nucleus splits into two smaller nuclei.

Answer 27

Fission