Question 1

Which reaction represents the melting of ice?

Accepted Answer

Melting is an endothermic process, meaning it requires energy to convert a solid into a liquid. Thus, the correct option is the one where energy is added to the solid form to produce the liquid form.

Question 2

A sample of sodium hydroxide dissolves in water, releasing heat to the surrounding water and causing the temperature to rise by 20 °C. If the heat change for the reaction is -300 J, what is the heat change for the surrounding water?

Accepted Answer

The heat change for the surrounding water is +300 J because the system (sodium hydroxide) releases heat (-300 J), which means the surroundings (water) absorb the same amount of heat but with the opposite sign, hence +300 J.

Question 3

A sample of ammonium chloride dissolves in water, absorbing heat from the surrounding water and causing the temperature to drop by 15 °C. If the heat change for the reaction is +200 J, what is the heat change for the surrounding water?

Accepted Answer

The heat change for the surrounding water is the opposite of the heat change for the reaction. Since the reaction absorbs heat (+200 J), the surrounding water loses that amount of heat, making the heat change for the water -200 J.

Question 4

The mixture of gas and air inside a cylinder reacts, releasing 400 kJ of total energy. If the system does 250 kJ of work on the piston, how much energy is released as HEAT?

Accepted Answer

According to the First Law of Thermodynamics, the total energy of a closed system is conserved. This means that the energy released by the reaction must be equal to the sum of the work done on the piston and the heat released to the surroundings.

Total Energy Released = Heat Released + Work Done

400 kJ = Heat Released + 250 kJ

Heat Released = 400 kJ - 250 kJ

Heat Released = 150 kJ

Therefore, the answer is A) 150 kJ.

Question 5

Chemists measure heat changes in reactions using a technique called:

Accepted Answer

Chemists measure heat changes in reactions using a technique called calorimetry. Calorimetry is the measurement of the heat flow into or out of a system for chemical and physical processes, such as chemical reactions, changes of state, and mixing of substances.

Question 6

The label on a two-pack of Reese's Peanut Butter cups lists 260 Calories (kcal) of stored chemical energy. What is this energy in kilojoules?

Accepted Answer

The answer of The label on a two-pack of Reese's...

Question 7

The signs of q and w for gasoline burning are, respectively:

Accepted Answer

When gasoline burns, energy is released to the surroundings, so q (heat) is negative. Work (w) is also negative because the system (gasoline) does work on the surroundings by expanding.

Question 8

The mixture of gas and air inside a cylinder reacts, releasing 300 kJ of heat. If the system does 150 kJ of work on the piston, what is the change in total energy?

Accepted Answer

The change in total energy can be calculated using the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. In this case, the heat released is 300 kJ and the work done is 150 kJ. Therefore, the change in total energy is:

ΔE = Q - W
ΔE = 300 kJ - 150 kJ
ΔE = 150 kJ

The change in total energy is positive, indicating that the system gained energy. Therefore, the best choice is A) 450 kJ.

Question 9

The law of conservation of energy states that, in chemical and physical changes:

Accepted Answer

The law of conservation of energy states that energy cannot be created or destroyed, only converted from one form to another. Therefore, it is not released to the surroundings or favors exothermic changes. It also does not increase the amount of energy in the universe since the total amount of energy remains constant.

Question 10

Changes in energy can take place in what two forms?

Accepted Answer

The answer of Changes in energy can take place in...

Question 11

How much heat is required to raise the temperature of 85.0 grams of water by 15.0 °C?

Accepted Answer

The heat required to raise the temperature of a substance can be calculated using the formula:

q = mcΔT

where q is the heat (in Joules), m is the mass of the substance (in grams), c is the specific heat capacity of the substance (in J/g°C), and ΔT is the change in temperature (in °C).

For water, c = 4.184 J/g°C.

Plugging in the given values:

q = (85.0 g)(4.184 J/g°C)(15.0°C)

q = 5,330 J

Therefore, the answer is D.

Question 12

A sample of ammonium chloride dissolves in water, absorbing heat from the surrounding water and causing the temperature to drop by 20 °C. If the heat change for the reaction is +300 J, what is the heat change for the surrounding water?

Accepted Answer

The heat change for the surrounding water is the opposite of the heat change for the reaction. Since the reaction absorbs heat (+300 J), the surrounding water loses that amount of heat, making the heat change for the water -300 J.

Question 13

Energy is often stored in the form of chemical bonds. This is a type of _____ energy.

Accepted Answer

Chemical bonds are a form of potential energy because they have the potential to release energy as they break and form new bonds. Kinetic energy is the energy of motion, while heat is the transfer of energy from one object to another due to a temperature difference.

Question 14

Which reaction represents the freezing of water?

Accepted Answer

The reaction that represents the freezing of water is when liquid water (H₂O (l)) loses energy and solidifies into ice (H₂O (s)). This process is represented by the equation: H₂O (l) F1F1F1S1→F1F1F10 H₂O (s) + energy. Option C matches this description.

Question 15

How much heat is released when 35.0 g of water are cooled by 40.0 °C?

Accepted Answer

The equation for calculating heat released is Q = mcΔT, where Q is the heat released, m is the mass of the substance, c is the specific heat capacity of the substance, and ΔT is the change in temperature. For water, c = 4.184 J/g°C. Plugging in the values, we get Q = (35.0 g)(4.184 J/g°C)(-40.0°C) = -5,860 J. The negative sign indicates that heat is released. Therefore, the answer is D.

Question 16

Which process is endothermic?

Accepted Answer

All of these processes are endothermic because they involve an absorption of energy from the surroundings. Melting, boiling, and evaporating all require energy input to break the bonds between molecules and change the phase of a substance.

Question 17

The label on a York Peppermint Patty lists 140 Calories (kcal) of stored chemical energy. What is this energy in kilojoules?

Accepted Answer

To convert from calories to kilojoules, we need to multiply by 4.184. 140 Calories x 4.184 = 586.96 kJ. Rounded to the nearest whole number, the answer is 590, which corresponds to choice C.

Question 18

A small Oreo Dairy Queen blizzard contains 550 kilocalories of stored chemical energy. What is this energy in kilojoules?

Accepted Answer

The answer of A small Oreo Dairy Queen blizzard contains...

Question 19

Which process is exothermic?

Accepted Answer

Melting, boiling, and evaporating are all endothermic processes, requiring energy to break intermolecular bonds.

Question 20

How much heat is required to raise the temperature of 125 grams of water by 10.0 °C?

Accepted Answer

The answer of How much heat is required to raise...

Quiz 8: Energy