IB Chemistry Energetics

What energy changes occur when chemical bonds are formed and broken?

• Energy is absorbed when bonds are formed and when they are broken.

• Energy is released when bonds are formed and when they are broken.

• Energy is absorbed when bonds are formed and released when they are broken.

• Energy is released when bonds are formed and absorbed when they are broken.

Tags

NGSS.HS-PS1-4

The temperature of a 2.0 g sample of aluminium increases from 25°C to 30°C.

How many joules of heat energy were added? (Specific heat of Al = 0.90 J g^–1K^–1)

• 0.36

• 2.3

• 9.0

• 11

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-2

Which statements about exothermic reactions are correct?

I. They have negative ΔH values.

II. The products have a lower enthalpy than the reactants.

III. The products are more energetically stable than the reactants.

• I and II only

• I and III only

• II and III only

• I, II and III

Tags

NGSS.HS-PS1-4

A sample of a metal is heated. Which of the following are needed to calculate the heat absorbed by the sample?

I. The mass of the sample

II. The density of the sample

III. The specific heat capacity of the sample

• I and II only

• I and III only

• II and III only

• I, II and III

Tags

NGSS.HS-PS3-1

Which statements are correct for an endothermic reaction?

I. The system absorbs heat.

II. The enthalpy change is positive.

III. The bond enthalpy total for the reactants is greater than for the products.

• I and II only

• I and III only

• II and III only

• I, II and III

Tags

NGSS.HS-PS1-4

The following thermochemical equation shows the formation of magnesium oxide from magnesium metal.

2Mg(s) + O₂(g)-> 2MgO(s) ΔH°= –1204 kJ

Which statement is correct for this reaction?

• 1204 kJ of energy are released for every mol of magnesium reacted.

• 602 kJ of energy are absorbed for every mol of magnesium oxide formed.

• 602 kJ of energy are released for every mol of oxygen gas reacted.

• 1204 kJ of energy are released for every two mol of magnesium oxide formed.

Tags

NGSS.HS-PS1-4

For which of the following is the sign of the enthalpy change different from the other three?

• CaCO₃(s) → CaO(s) + CO₂(g)

• Na(g) → Na⁺(g) + e^–

• CO₂(s) → CO₂(g)

• 2Cl(g) → Cl₂(g)

Tags

NGSS.HS-PS1-4

Which of the quantities in the enthalpy level diagram below is (are) affected by the use of a catalyst?

• I only

• III only

• I and II only

• II and III only

Tags

NGSS.HS-PS1-4

A simple calorimeter was used to determine the enthalpy of combustion of ethanol. The experimental value obtained was –920 kJ mol^–1. The Data Booklet value is –1371 kJ mol^–1.

Which of the following best explains the difference between the two values?

• incomplete combustion of the fuel

• heat loss to the surroundings

• poor ventilation in the laboratory

• inaccurate temperature measurements

The average bond enthalpy for the C―H bond is 412 kJ mol^–1. Which process has an enthalpy change closest to this value?

• CH₄(g) → C(s) + 2H₂(g)

• CH₄(g) → C(g) + 2H₂(g)

• CH₄(g) → C(s) + 4H(g)

• CH₄(g) → CH₃(g) + H(g)

Tags

NGSS.HS-PS1-4