Thermochemistry

The potential energy diagram of a reaction is shown. Which statement below is correct relating to this reaction?

• #1 represents the enthalpy change for this exothermic reaction.

• #2 represents the enthalpy change for this endothermic reaction.

• #3 represents the enthalpy change for this endothermic reaction.

• #4 represents the enthalpy change for this exothermic reaction.

Tags

NGSS.HS-PS1-4

During an exothermic reaction, heat content in the surroundings increases because

• heat energy is destroyed during reactions

• the reaction absorbs heat energy

• the energy contained in the reactants is lower then the products

• the energy contained in the products is lower than the reactants

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

The diagram represents two solids and the temperature of each. What occurs when the two solids are placed in contact with each other?

• Heat energy flows from solid A to solid B. Solid A decreases in temperature

• Heat energy flows from solid A to solid B. Solid A increases in temperature

• Heat energy flows from solid B to solid A. Solid B decreases in temperature.

• Heat energy flows from solid B to solid A. Solid B increases in temperature.

Tags

NGSS.HS-PS3-4

The amount of heat energy required to change the temperature of 12 g of gold from 45°C to 15°C is -47 J. What is the specific heat capacity of gold?

• 0.13 J/(g°C)

• 17,000 J/(g°C)

• 1600 J/(g°C)

• 0.065 J/(g°C)

Tags

NGSS.HS-PS3-4

The graph represents the uniform heating of a substance, starting with the substance as a solid below its melting point. Which line segment listed below represents an increase in potential energy and no change in average kinetic energy?

• Line segment AB

• Line segment BC

• Line segment CD

• Line segment EF

Tags

NGSS.MS-PS1-4

NGSS.MS-PS3-2

A cast iron skillet is used to fry bacon. For optimal frying, the pan must be heated to about 178 ^oC from a room temperature of 22.0 ^oC. It is known that 1.58 x 10⁵ J of heat energy are absorbed by the pan to reach the desired temperature and the specific heat of iron is 0.450 J/g ^oC. What must the mass of the skillet be?

• 12.7 kg

• 2.25 kg

• 110 kg

• 1.97 kg

Tags

NGSS.HS-PS3-1

Experimental Set-up for Calories in a Chocolate Chip Cookie Students designed an experiment to determine the amount of calories in a chocolate chip cookie. A ring stand was used with a clean aluminum soda can hung from the ring that was partially filled with a known mass of water. A thermometer was placed inside the can so that it measured the temperature of the water but did not touch any part of the metal can. Once set-up was complete, an initial water temperature was taken. The cookie was then lit on fire and allowed to completely burn. A final temperature of the water was measured.

Refer to the experimental set-up for calories in a chocolate chip cookie. How does this experiment allow students to measure the calories in a cookie?

• The difference in masses before and after the cookie is burned is calculated, then converted into heat energy.

• Heat energy from the burning cookie is transferred to the water. The change in water temperature is used to calculate the heat energy from the cookie.

• Data from the amount of time for the cookie to burn and the temperature change are used to calculate the heat energy from the cookie.

• The cookie is burned until the water reaches a boiling temperature, then masses are compared to calculate the heat energy from the cookie.

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

When methane, CH4, and oxygen, O2, are mixed in a stove and ignited, a lovely blue flame results. The balanced equation is: CH₄(g) + 2O₂(g) 2H₂O(g) + CO₂(g) What can be said about the energy involved in this chemical reaction?

I. The average kinetic energy of the products is greater than that of the reactants.

II. The chemical energy stored in the reactants is greater than the chemical energy stored in the products.

III. Chemical energy in the reactants is changed into heat energy and light energy.

• I only

• II only

• III only

• I, II, and III

Tags

NGSS.HS-PS1-4

The enthalpy change for the reaction
C(s, graphite) + 1⁄2O₂(g) --> CO(g) cannot be measured directly since some carbon dioxide is always formed in the reaction.
It can be calculated using Hess’s Law and the enthalpy changes of combustion of graphite and of carbon monoxide.
C(s, graphite) + O₂(g) --> CO₂    ΔH=-394 kJmol^–1
CO(g) + 1⁄2O₂(g) --> CO₂  ΔH=-283 kJmol^–1  
The enthalpy change for the reaction of graphite with oxygen to give carbon monoxide is 

• -677 kJmol^–1 
• +111 kJmol^–1 
• -111 kJmol^–1 
• +677 kJmol^–1 

Tags

NGSS.HS-PS1-4

The enthalpy change for the reaction, ∆H_r , is equal to 

• ∆H₁ + ∆H₂
• ∆H₁ - ∆H₂
• -∆H₁ - ∆H₂
• -∆H₁ + ∆H₂

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1