The specific heat of aluminum is 0.900 J/g°C. How much heat is required to raise the temperature of a 30.0g block of aluminum from 25.0°C to 75.0°C?

A. 0.540J
Incorrect. q=mC∆T, q=(30.0g)(0.900J/g°C)(50°C), q=1350J

B. 1.50J
Incorrect. q=mC∆T, q=(30.0g)(0.900J/g°C)(50°C), q=1350J350J

C. 1350J
Correct! q=mC∆T, q=(30.0g)(0.900J/g°C)(50°C), q=1350J

D. 1670J
Incorrect. q=mC∆T, q=(30.0g)(0.900J/g°C)(50°C), q=1350J350J

Given the balanced equation representing a reaction at 101.3 kPa and 298K —

N₂(g) + 3H₂(g) → 2NH₃(g) + 91.8kJ

A. It is exothermic and ∆H equals -91.8kJ.
Correct! Exothermic reactions have energy as a product and a negative ∆H.

B. It is exothermic and ∆H equals +91.8 kJ.
Incorrect. Exothermic reactions have a negative ∆H.

C. It is endothermic and ∆H equals -91.8 kJ.
Incorrect. Endothermic reactions have a positive ∆H and have energy as a reactant.

D. It is endothermic and ∆H equals +91.8 kJ.
Incorrect. Endothermic reactions have energy as a reactant.

The table below shows the specific heat capacity of four substances.

For an equal mass of each substance, which one will require the least amount of heat to raise its temperature from 40°C to 50°C?

A. water
Incorrect. Water would require the most amount of heat (energy) to raise it’s temperature.

B. copper
Incorrect. It would take 0.39 J for each degree change in copper. There is a substance that requires less heat (energy) than copper.

C. gold
Correct! The smaller the specific heat the less heat (energy) that is needed to raise the temperature.

D. silver
Incorrect. It would take 0.24 J for each degree change in silver. There is a substance that requires less heat (energy) than silver.

2CuO(s) → Cu₂O(s) + 1 2O₂(g)

A. 141.5
Correct! ΔHrxn = [HCu₂O + 1 2(HO₂)] – 2(HCuO)
= [-170.7 + 1 2(0)] – 2(-156.1)
= 141.5 kJ

B. 14.6
Incorrect. ΔHrxn = [HCu₂O + 1 2(HO₂)] – 2(HCuO)
= [-170.7 + 1 2(0)] – 2(-156.1)
= 141.5 kJ

C. -14.6
Incorrect. ΔHrxn = [HCu₂O + 1 2(HO₂)] – 2(HCuO)
= [-170.7 + 1 2(0)] – 2(-156.1)
= 141.5 kJ

D. -141.5
Incorrect. ΔHrxn = [HCu₂O + 1 2(HO₂)] – 2(HCuO)
= [-170.7 + 1 2(0)] – 2(-156.1)
= 141.5 kJ

2Al(s) + 3Cl₂(g) → 2AlCl₃(s)   ?H = -1391 kJ

When a 20.0g sample of chlorine reacts with excess aluminum, how much energy will be released as heat?

A. 1739 kJ
Incorrect. Did you use dimensional analysis?

B. 869 kJ
Incorrect. Did you use dimensional analysis?

C. 580 kJ
Incorrect. Did you use dimensional analysis?

D. 290 kJ
Correct!