Energetics Review

Which statement describes an endothermic reaction?

• The bonds broken are stronger than the bonds formed.

• The enthalpy of the reactants is higher than the enthalpy of the products.

• The temperature of the surroundings increases.

• The products are more stable than the reactants.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

What is the enthalpy change, in J, when 5 g of water is heated from 10°C to 18°C?

Specific heat capacity of water: 4.18 kJ kg⁻¹ K⁻¹

• 5 × 4.18 × 8

• 5 × 10⁻³ × 4.18 × 8

• 5 × 4.18 × (273 + 8)

• 5 × 10⁻³ × 4.18 × (273 + 8)

Tags

NGSS.HS-PS3-1

Which change of state is exothermic? 

• CO₂(s) → CO₂(g)

• H₂O(l) → H₂O(g) 

• NH₃(g) → NH₃(l) 

• Fe(s) → Fe(l)

Which statement is correct for this reaction?

Fe₂O₃ (s) + 3CO (g) → 2Fe (s) + 3CO₂ (g)       ΔH = −26.6 kJ

• 13.3 kJ are released for every mole of Fe produced.

• 26.6 kJ are absorbed for every mole of Fe produced.

• 53.2 kJ are released for every mole of Fe produced.

• 26.6 kJ are released for every mole of Fe produced.

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which is correct when Ba(OH)₂ reacts with NH₄Cl?

Ba(OH)₂ (s) + 2NH₄Cl (s) → BaCl₂ (aq) + 2NH₃ (g) + 2H₂O (l)       ΔH^Θ = +164 kJ mol⁻¹

• A

• B

• C

• D

Tags

NGSS.HS-PS1-2

NGSS.HS-PS1-4

The enthalpy of combustion of ethanol is determined by heating a known mass of tap water in a glass beaker with a flame of burning ethanol.

Which will lead to the greatest error in the final result?

• Assuming the density of tap water is 1.0 g cm⁻³

• Assuming all the energy from the combustion will heat the water

•  Assuming the specific heat capacity of the tap water is 4.18 J g⁻¹ K⁻¹

•  Assuming the specific heat capacity of the beaker is negligible

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4

When equal masses of X and Y absorb the same amount of energy, their temperatures rise by 5 °C and 10 °C respectively. Which is correct?

• The specific heat capacity of X is twice that of Y.

• The specific heat capacity of X is half that of Y.

• The specific heat capacity of X is one fifth that of Y.

• The specific heat capacity of X is the same as Y.

A student obtained the following data to calculate qq, using q=mcΔT

m=20.2g (±0.2g)

ΔT=10°C (±1°C)

c=4.18Jg−1K−1

What is the percentage uncertainty in the calculated value of q?

• 0.2

• 1.2

• 11

• 14

Tags

NGSS.HS-PS3-1

What is the heat change, in kJ, when 100.0 g of aluminium is heated from 19.0 °C to 32.0 °C?

Specific heat capacity of aluminium: 0.90 J g⁻¹K⁻¹

• 0.90×100.0×13.0

• 0.90×100.0×286

• 0.90×100.0×13.0 / 1000

• 0.90×100.0×286 / 1000

Tags

NGSS.HS-PS3-4

The enthalpy of combustion of a fuel was determined using the calorimeter shown. The final result was lower than the literature value.

Which factors could have contributed to this error?

I.   Not all heat from the combustion was transferred to the calorimeter.

II.  Incomplete combustion occurred.

III. The temperature probe touched the bottom of the calorimeter.

• I and II only

• I and III only

• II and III only

• I, II and III

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-4