Thermochemistry Pt 1

Question 1

Energy

Answer 1

the capacity to do work or transfer heat

Question 2

thermochemistry

Answer 2

the study of heat and energy in chemical reactions

Question 3

Kinetic energy

Answer 3

KE = (1/2)mv^2

Question 4

Potential energy

Answer 4

energy related to an object’s position

Question 5

Main rule of energy

Answer 5

energy can be converted from one form to another

Question 6

Common units of energy

Answer 6

JOULE (J)
- 1 calorie = 4.184 J

Question 7

System

Answer 7

definition of the source of energy (container with chemical reactants and products)

Question 8

Surroundings

Answer 8

the rest of the universe
- it is important to clearly define the system and surroundings when discussing transfers of energy

Question 9

Open System

Answer 9

both matter and energy can move between the system and its surroundings
- EX: fireplace with burning wood

Question 10

Closed System

Answer 10

energy but not matter can move between the system and its surroundings
- ED: pressure cooker

Question 11

Isolated System

Answer 11

neither matter nor energy can leave or enter the system
- EX: thermos

Question 12

Work (W)

Answer 12

the energy resulting from a force acting on an object over a distance

Question 13

Heat (q)

Answer 13

the flow of energy that causes a temperature change in an object or its surrounding

Question 14

When is work positive?

Answer 14

when work is done ON the system

Question 15

When is work negative?

Answer 15

when work is done BY the system

Question 16

First 1st of Thermodynamics: Law of Conservation of Energy

Answer 16

energy cannot be created or destroyed, just transferred from one form to another
- the energy of the universe is CONSTANT

Question 17

Internal Energy (U)

Answer 17

the sum of all kinetic and potential energies of the particles within a system
- usually measured in changes in internal energy:

ΔU=Ufinal-Uinitial

Question 18

1st Law of Thermodynamics Equation

Answer 18

ΔU = q + w

all the heat and work in the system !!!

Question 19

What is ΔU when W and Q are positive?

Answer 19

ΔU is positive

Question 20

What is ΔU when W is negative and Q is negative?

Answer 20

ΔU is negative

Question 21

What is ΔU when Q is negarive and W is positive?

Answer 21

relative magnitudes will determine if ΔU is negative or positive

Question 22

State function

Answer 22

current state of a system and is INDEPENDENT OF THE PATH TAKEN to achieve its value
- the U of the system is independent of the pathway taken to achieve it
- internal energy IS a state function

Question 23

Path function

Answer 23

• work and heat are path functions
• the value depends on the sequence of steps that move a system from its initial to final state
• do NOT describe the current state of a system

Question 24

Pressure-Volume Work

Answer 24

the work done by a system (usually gas) when its volume changes under the influence of an external pressure

Question 25

Pressure-Volume Work Equation

Answer 25

W = -PΔV (AKA: -P(Vfinal-Vinitial))

Question 26

Pressure-Volume and Work

THERE MUST BE A CHANGE IN VOLUME FRO WORK TO OCCUR

Answer 26

• When gas increases in volume, the change in volume is positive, and the value of work is NEGATIVE as the system is DOING WORK ON THE SURROUNDINGS
• When gas decreases in volume, the change in volume is negative, and the value of work is POSITIVE as the surroundings are DOING WORK ON THE SYSTEM

Question 27

Enthalpy (H)

Answer 27

H = U + PV

Question 28

Change in Enthalpy

Answer 28

ΔH = ΔU + PΔV
ΔH = (q.p) (A change in enthalpy is the flow of heat at constant pressure)

Question 29

Endothermic Process

Answer 29

reactions that absorb heat from the surroundings
- ΔH is POSITIVE

Question 30

Exothermic Processes

Answer 30

reactions that release heat form the system to the surroundings
- Δ is NEGATIVE