Test #1 Gases and Thermochemistry

Question 1

What are the general characteristics of gases?

Answer 1

No definite volume.
No definite shape.
Gases can be expanded infinitely.
Gases occupy containers uniformly and completely.
There is a large distance between gas molecules, relative to the size of the molecule.
Gases diffuse and mix rapidly and randomly.
Gases are the most disordered of the phases of matter.

Question 2

Define pressure.

Answer 2

Force exerted on the walls of a container by collisions from gas molecules.

Question 3

Define ideal gas law.

Answer 3

Explains the relationships between the properties of gases.

Question 4

The capacity to do work or transfer heat.

Answer 4

Energy

Question 5

The form of energy that flows between objects because of their difference in temperature.

Answer 5

Heat

Question 6

Classification of Energy

Answer 6

Potential energy:
Gravitational energy: PE due to position.
Elastic PE: PE stored in springs.
Chemical PE: PE stored in chemical bonds.
Other Forms of Energy:
Thermal energy is associated with temperature.
Electrical energy is associated with electrical current.
Chemical energy is associated with the positions of electrons and nuclei.

Question 7

Define internal energy.

Answer 7

Sum of the potential and kinetic energy of all particles in a system.

Question 8

Internal energy of a chemical system depends on…

Answer 8

Number of particles.
Type of particles.
Temperature.
The higher the T, the higher the internal energy.

Question 9

Define thermodynamics.

Answer 9

The science of energy transfer as heat.

Question 10

Thermodynamics depends on…

Answer 10

The law of conservation of enerfy(first law of thermodynamics: total energy of the universe is constant.)

Question 11

What are the two types of energy transfer?

Answer 11

Endothermic: energy enters the system from the surroundings. The energy of the system increases as the energy of the surrounding decreases.
Exothermic: Energy leaves the system and goes into the surroundings. The energy of the system goes down, while the energy of the surroundings goes up.

Question 12

The amount of energy required to raise an object’s temperature by 1.0 Celsius

Answer 12

Heat capacity.

Question 13

The amount of energy required to raise the temperature of 1g of matter by 1 Celsisus.

Answer 13

Specific heat.

Question 14

Define Calorimetry

Answer 14

A quantitative method to determine heat flow between two systems and their surroundings. Systems can be about physical (phase) changes or chemical (reactions) changes.

Question 15

If the Hfinal is less than the H initial, what does that mean?

Answer 15

If Hfinal < Hinitial, then ∆H is designated with a negative sign.
Reaction is exothermic.

Question 16

Define Hess’ Law.

Answer 16

The change in enthalpy for a stepwise process is the sum of the enthalpy changes of the steps.

Question 17

Enthalpy reaction can be determined in two ways:

Answer 17

Applying Hess’ Law using two or more reactions with ∆H known for each reaction.

Using standard enthalpy of formation (〖∆𝐻〗_𝑓^0) for each reactant and product. ∆H is the difference in enthalpy between products and reactants

Question 18

Three quantitative relationships to the reactions used in Hess’ Law:

Answer 18

If the reaction is multiplied by some factor, then ∆Hrxn is also multiplied by that factor.

If the direction of the reaction is reversed, the sign of ∆Hrxn is changed.

If the target reaction can be expressed as the sum of a series of steps, the ∆Hrxn for the target reaction is the sum of the ∆Hrxn of the steps.

Question 19

Define Standard Enthalpy of Formation

Answer 19

The change in enthalpy when 1 mole of a substance is formed from its constituent elements in their standard states.

Question 20

The law of ______ states that energy that can be neither created or destroyed.

Answer 20

Conservation of energy.

Question 21

What does it mean if the delta H for a reaction has a positive/negative sign?

Answer 21

Positive: The reaction is endothermic.
Negative: The reaction is exothermic.

Question 22

If Hfinal is greater than the Hinitial, what does it mean?

Answer 22

If Hfinal > Hinitial, then ∆H is designated with a positive sign.
Reaction is endothermic.