SAT Chemistry Practice Test: Energy and Chemical Reactions

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Question 7 questions

Time 5 minutes

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1. Two systems at different temperatures come in contact. The heat will flow from the system at

A. 30°C to a system at 317 K
B. 40°C to a system at 323 K
C. 50°C to a system at 303 K
D. 60°C to a system at 358 K
E. 70°C to a system at 370 K

2. How many joules of heat are released by a 150-gram sample of water that that cools from 25°C to 5°C? (c for H2O is 4.18 J/gK)

A. 78,375 joules
B. 83.6 joules
C. 720 joules
D. 627 joules
E. 12,540 joules

3. Calculate the number of joules required to completely evaporate 18 grams of water at 98°C. (Hv = 2259 J/g and c = 4.18 J/gK)

A. 40,812 joules
B. 40,512 joules
C. 150 joules
D. 40,662 joules
E. 6.12 × 106 joules

4. Which process below has been described correctly for a temperature above 274K?

A. H2O(l) → H2O(s) is exothermic and spontaneous.
B. H2O(l) → H2O(s) is endothermic and spontaneous.
C. H2O(g) → H2O(l) is endothermic and spontaneous.
D. H2O(s) → H2O(l) is endothermic and spontaneous.
E. H2O(s) → H2O(l) is exothermic and spontaneous.

5. Based on Gibbs Free Energy equation ΔG =ΔH-TΔS, a process will occur spontaneously when

A. ΔG is positive and ΔS is positive
B. ΔH is positive and ΔT is negative
C. ΔH is negative and ΔS is positive
D. ΔH is negative and ΔS is negative
E. ΔG is positive and ΔS is negative

6. The overall reaction: A + B + 1.5C →D has three individual reactions that take place,

Step 1: A + 2B → E
Step 2: F → B + C
Step 3: ?
What is the reaction that takes place in Step 3?

A. D + F → C + E
B. E + 5/2C → D + F
C. D + 3/2C → A + E
D. B + C → F + E
E. A + B + 1.5C → D

7. Calculate the heat for the overall reaction:

Mg(s) + 1/2O2 → MgO(s) given the heats of reaction below:

Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
ΔH = -143 kJ
MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(g)
ΔH = -216 kJ
H2(g) + 1 /2O2 → H2O(l)
ΔH = -285 kJ

A. -644 kJ
B. -212 kJ
C. +644 kJ
D. -74 kJ
E. +74 kJ