Thermochemistry

Question 1

What is energy?

Answer 1

Ability to do work or transfer heat

Question 2

What does work do?

Answer 2

Energy used to cause an object that has mass to move.

Question 3

What does heat do?

Answer 3

Energy used to cause the temperature of an object to rise.

Question 4

What is a system?

Answer 4

the molecules we want to study (thing you want to study

Question 5

What are the surroundings?

Answer 5

are everything else

Question 6

What is the first law of thermodynamics?

Answer 6

the total energy of the universe is a constant; if the system loses energy, it must be gained by the surroundings, and vice versa.

Question 7

What is an open system?

Answer 7

can exchange both matter and energy with an outside system.

Question 8

What is a closed system?

Answer 8

exchange energy but not matter with outside system

Question 9

What is an isolated system?

Answer 9

Can exchange neither energy or matter with outside

Question 10

What is the second law of thermodynamics?

Answer 10

• energy can be transferred as heat
• Heat flows from warmer objects to cooler until thermal equilibrium

Question 11

What is Q?

Answer 11

the amount of energy required to raise the temperature of a substance by 1 Celsius

Question 12

What is c?

Answer 12

the amount of energy required to raise the temperature of 1 g of a substance by 1 K.

Question 13

What is internal energy (E)?

Answer 13

the sum of all kinetic and potential energies of all components of the system

Question 14

What is enthalpy?

Answer 14

total heat content of a system

Question 15

What is endothermic?

Answer 15

heat being absorbed

Question 16

What is exothermic?

Answer 16

Heat being released

Question 17

Why do some energy not let temperature rise?

Answer 17

Some of the energy is used to change in states

Question 18

When water turns into steam, why is it at the same temperature for a long time?

Answer 18

Because the bonds are being broken

Question 19

What is Hess’s Law?

Answer 19

“If a reaction is carried out in a series of steps, ΔH for the overall reaction will be equal to the SUM of
the enthalpy changes for the individual steps.”

Question 20

What is bond dissociation?

Answer 20

energy needed to break one mole of the bond to give separated atoms - everything being in the gas state

Question 21

How to measure reaction rate?

Answer 21

Anything over time (depletion of reactant or formation of products)

Question 22

How to measure concentration?

Answer 22

1. Change in volume
2. remove small samples of a reaction mixture and perform titration
3. use of a spectrophotometer
4. Measure remaining mass

Question 23

What increases rates of reaction?

Answer 23

1. as concentration of reactants increase
2. as temp increased
3. with a catalyst -> lower activation energy
4. as reactant surface area increases

Question 24

What is the average rate?

Answer 24

Reaction rate over time

Question 24

What is the average rate?

Answer 24

Reaction rate over time

Question 25

What is instantaneous rate?

Answer 25

Reaction rate at any given time

Question 26

What makes an effective collision?

Answer 26

1. correct geometry
2. sufficient energy (being absorbed or released)

Question 27

What is activation energy?

Answer 27

Minimum amount of kinetic energy the reactants must have in order to react.

Question 28

What affects the reaction rate?

Answer 28

1. Nature of Reactants
2. Concentration
3. Temperature
4. Catalyst
5. Surface Area (Particle Size)
6. Mixing (Stirring)

Question 29

How does the nature of reactants affect rate?

Answer 29

Some reactants are more reactive than others

Question 30

How does concentration affect rate?

Answer 30

Higher concentration = more collisions

Question 31

How does temperature affect rate?

Answer 31

Higher temperature means faster collisions

Question 32

How does catalyst effect rate?

Answer 32

Lowers the activation energy

Question 33

How does particle size affect the rate?

Answer 33

Smaller the particle size = faster the rate

Question 34

What is rate law?

Answer 34

how changes in the amount of a substance affect the rate of a chemical reaction

Question 35

What does rate law tell us?

Answer 35

• shows the relationship between the reaction rate and the concentrations of reactants
• k is a constant that has a specific value for each reaction.
• The value of k is determined experimentally
• Exponents tell the order of the reaction with respect to each reactant.

Question 36

What are elementary steps?

Answer 36

A reaction intermediate (or, reactants) is converted into the next reaction intermediate (or, products)

Question 37

What is a reaction’s molecularity defined by?

Answer 37

the number of particles that participate as reactants in an elementary step.

Question 38

Rate law vs overall rate law

Answer 38

Rate law: for all the steps (1 each)
Overall rate law is for the whole overall reaction
- Gives the R.D.S

Question 39

What is the reaction mechanism?

Answer 39

sequence of actual events that take place as reactant molecules are converted into products