Question

NEED HELP ASAP 1-4

and has a question. 1) A chemical reaction that releases heat to the surroundings is said to be _AH at constant pressure. A) endothermic, positive B) endothermic, negative C) exothermic, positive D) exothermic, neutral E) exothermic, negative kJ of heat are transferred when 161.8 2) The value of AHº for the reaction below is -72 kJ. g of HBr is formed in this reaction. H2(g) + Br2 (g) → 2HBr (g) A) 54 B) 36 C) 144 D) 0.44 E) 72 3) Which of the following reactions is the reaction for standard enthalpy of formation of ammonia gas, NH3(g)? A) N2(g) + 3H2(g) + 2NH3(g) B) 4NO(g) + 6H2O(g) + 4NH3(g) + 502(g) C) 1/2 N2(g) + 3/2 H2(g) - NH3(g) D) 1/2 N2(s) + 3/2 H2(s) - NH3(g) E) 2NH3(g) + N2(g) + 3H2(g) 4) A 32.0 g sample of a metal at 76.1 °C is placed in 45.7 g of water at 19.2 °C in a coffee-cup calorimeter. The temperature of water increased to 27.3°C. What is the specific heat of the metal? The specific heat of water is 4.184 J/g-°C. A) 0.44 J/g-°C B) 0.45 J/g-°C C) 1.20 J/g-°C D) 0.99 J/g-°C E) 0.74 J/g-°C

Answer 1

1)

When system releases heat, the reaction is said to be exothermic and sign of ΔH is negative

Answer: E

2)

Molar mass of HBr,

MM = 1*MM(H) + 1*MM(Br)

= 1*1.008 + 1*79.9

= 80.908 g/mol

mass(HBr)= 161.8 g

use:

number of mol of HBr,

n = mass of HBr/molar mass of HBr

=(1.618*10^2 g)/(80.91 g/mol)

= 2 mol

Since Δ H is negative, heat is released

when 2 mol of HBr reacts, heat released = 72 KJ

Answer: E

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