Enthalpy of Reaction

The heat of reaction (△H) is equal to the

• entropy of the reactants minus the entropy of the products

• entropy of the products minus the entropy of the reactants

• heat content of the reactants minus the heat content of the products

• heat content of the products minus the heat content of the reactants

Tags

NGSS.HS-PS3-1

The change of reactants into products will always be spontaneous if the products, compared to the reactants, have

• lower enthalpy and lower entropy

• higher enthalpy and lower entropy

• higher enthalpy and higher entropy

• lower enthalpy and higher entropy

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

• ∆H₁ + ∆H₂

• -∆H₁ - ∆H₂

• ∆H₁ - ∆H₂

• -∆H₁ + ∆H₂

Tags

NGSS.HS-PS1-4

The enthalpies of combustion of C(s), H2(g) and C4H9OH(l) (in kJmol^-1) are as follows

C(s) + O₂(g) -> CO₂(g) ∆H=a

H₂(g) + ½O₂(g) -> H₂O(l) ∆H=b

C₄H₉OH(l) + 6O₂(g) -> 4CO₂(g) + 5H₂O(l) ∆H=c

What is the enthalpy change for the reaction shown below?

4C(g) + 5H₂(l) + ½O₂(g) -> C₄H₉OH(l)

• c – 4a – 5b

• 4a + 5b - c

• 2a + 10b - c

• 2a + 5b + c

The standard enthalpy changes of combustion of carbon, hydrogen and methane are shown in the table.

Which one of the following expressions gives the correct value for the standard enthalpy change of formation of methane in kJ mol

^–1?

C(s) + 2H

₂(g) → CH₄(g)

• 394 + (2 × 286) – 891

• –394 – (2 × 286) + 891

• 394 + 286 – 891

• –394 – 286 + 891

Tags

NGSS.HS-PS1-2

NGSS.HS-PS1-4

The following equations show the oxidation of carbon and carbon monoxide to carbon dioxide. C(s) +O2(g) → CO2(g) ΔH = –x kJ mol–1 CO(g) + O2(g) → CO2(g) ΔH = –y kJ mol–1 What is the enthalpy change, in kJ mol–1, for the oxidation of carbon to carbon monoxide? C(s) + O2(g) → CO(g)

• x + y

• -x - y

• y - x

• x - y

Tags

NGSS.HS-PS3-1

Grace, Noah, and Abigail were baking a cake together. They noticed a change in the energy of the system during the chemical reaction between the ingredients. What is this change called?

• A decrease in energy during a chemical reaction

• An increase in energy during a chemical reaction

• The randomness of a chemical

• The stability of a chemical

Answer explanation

The change in energy during a chemical reaction, as observed by Grace, Noah, and Abigail, is called an increase in energy. This occurs when the energy of the system increases as the ingredients interact and form new bonds, resulting in the formation of the cake.

Tags

NGSS.HS-PS1-4

Benjamin and Charlotte are working on a chemistry project together. They observe an endothermic reaction when they mix two chemicals. What is the result of this endothermic reaction?

• An increase in energy

• A decrease in energy

• An explosion

• An increase in randomness

Answer explanation

In an endothermic reaction, energy is absorbed from the surroundings, causing an increase in energy. When Benjamin and Charlotte mix the two chemicals, they observe this type of reaction, which results in an increase in energy, making it the correct choice.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the following statements best describes the enthalpy of reaction?

• The total energy absorbed during a reaction

• The total energy released during a reaction

• The difference between the enthalpy of the products and the enthalpy of the reactants

• The sum of the enthalpy of the reactants and products

In an exothermic reaction, the enthalpy of the products is:

• Greater than the enthalpy of the reactants

• Less than the enthalpy of the reactants

• Equal to the enthalpy of the reactants

• Unrelated to the enthalpy of the reactants

Tags

NGSS.HS-PS1-4