Unit 4

Question 1

physical state or phase

Answer 1

a condition of a sate of matter

Question 2

physical change

Answer 2

a change of substance that does not involve a change in identity

Question 3

heat

Answer 3

the energy transfer between two samples of matter because of a change in temperature

Question 4

temperature

Answer 4

a measure of the average kinetic energy in a sample of matter

Question 5

absorb

Answer 5

take in or soak up in a chemical or physical reaciton

Question 6

system v.s. surrounding

Answer 6

a system has boundaries whereas a surrounding does not

Question 7

specific heat capacity

Answer 7

the amount of energy required to raise the temperature by one kelvin or celsius

Question 8

latent heat

Answer 8

the amount of energy needed to change a solid to a liquid or vapor or from a liquid to a vapor without a change in temperature

Question 9

enthalpy

Answer 9

enthalpy or H is the heat content of a reaction. Mnemonic: H stands for heat.

Question 10

calorimeter

Answer 10

a device used to measure the amount of heat absorbed or reflected in a chemical or physical change

Question 11

calorie

Answer 11

the amount of energy needed to raise 1g of water by 1 C

Question 12

Conservation of energy

Answer 12

The total energy of an isolated system remains constant.
The total energy of a closed or open system plus the total energy of its surroundings is constant.
Total energy is neither gained nor lost, it is merely transferred between the system and its surroundings.

Question 13

thermodynamic system

Answer 13

Isolated system: no exchange of heat, work, or matter with the surroundings.
Closed system: exchange of heat and work, but not matter with the surroundings.
Open system: exchange of heat, work and matter with the surroundings.

Question 14

heat capacity

Answer 14

the amount of heat required to raise the temperature of something by 1 °C.

Question 15

q = mcΔT

Answer 15

q is heat absorbed / heat input, m is mass, c is specific heat, and ΔT is change in temperature.
This formula only works if no phase change is involved.
Different phases have different specific heats, and on top of that, a phase change requires extra energy such as heat of fusion and heat of vaporization, which is why the above formula does not work across different phases.

Question 16

Hess’ law of heat summation

Answer 16

ΔHrxn = Δ(ΔHf) = sum of ΔHf (products) - sum of ΔHf (reactants)
The enthalpy of a given chemical reaction is constant, regardless of the reaction happening in one step or many steps.

Question 17

state f(x)

Answer 17

A state function is path-independent and depends only on the initial and final states.
State functions include: ΔH (enthalpy), ΔS (entropy), ΔG (free energy change), ΔU (internal energy change).
State function is also called state quantity, or function of state.

Question 18

standard state

Answer 18

The standard state of a chemical substance is its phase (solid, liquid, gas) at 25.0 °C and 1 atmosphere pressure. This temperature/pressure combo is often called “room conditions.”

Question 19

Work

Answer 19

refers to an activity involving a force and movement in the direction of the force. A force of 20 newtons pushing an object 5 meters in the direction of the force does 100 joules of work.

Question 20

Energy

Answer 20

is the capacity for doing work. You must have energy to accomplish work - it is like the “currency” for performing work. To do 100 joules of work, you must expend 100 joules of energy.

Question 21

heat v temperature

Answer 21

Heat is the total energy of molecular motion in a substance while temperature is a measure of the average energy of molecular motion in a substance. Heat energy depends on the speed of the particles, the number of particles (the size or mass), and the type of particles in an object. Temperature does not depend on the size or type of object. For example, the temperature of a small cup of water might be the same as the temperature of a large tub of water, but the tub of water has more heat because it has more water and thus more total thermal energy.

Question 22

chemical energy v potential energy

Answer 22

Chemical energy is energy that is stored in chemicals, such as sugar and gasoline. As chemical energy is stored energy, it is a type of potential energy, which is energy stored in objects due to their location. An easy example of potential energy would be that of a bike on top of a hill where the bike’s position is elevated and has the ability to roll down the hill. In the case of chemicals, the position refers to the various atoms that exist together within the chemical.

Question 23

specific heat v heat capacity

Answer 23

Heat Capacity: ratio of the amount of energy absorbed to the associated temperature rise.
• Example: if it takes 10 calories to raise the temperature of a glass of water by 2 °C, then the
heat capacity of the glass of water is 10 calories/2°C = 5 calories per °C.
• Specific Heat: the heat capacity of a substance per unit mass
• Example: for water, it takes 1 calorie to raise the temperature of 1 gram of water by 1°C. So
the specific heat for water is 1cal/gram °C

Question 24

calorimetry

Answer 24

A calorimeter is a device used to measure the quantity of heat transferred to or from an object.
The assumption behind the science of calorimetry is that the energy gained or lost by the water is equal to the energy lost or gained by the object under study. So if an attempt is being made to determine the specific heat of fusion of ice using a coffee cup calorimeter, then the assumption is that the energy gained by the ice when melting is equal to the energy lost by the surrounding water. It is assumed that there is a heat exchange between the iceand the water in the cup and that no other objects are involved in the heat exchanged. This statement could be placed in equation form as

Question 25

coffee cup calorimeter

Answer 25

The role of the Styrofoam in a coffee cup calorimeter is that it reduces the amount of heat exchange between the water in the coffee cup and the surrounding air. The value of a lid on the coffee cup is that it also reduces the amount of heat exchange between the water and the surrounding air. The more that these other heat exchanges are reduced, the more true that the above mathematical equation will be. Any error analysis of a calorimetry experiment must take into consideration the flow of heat from system to calorimeter to other parts of the surroundings. And any design of a calorimeter experiment must give attention to reducing the exchanges of heat between the calorimeter contents and the surroundings.