Study the reactions. C2H2 (g)+2H2 (g)→C2H6 (g)ΔH=−75 kcal C2H4 (g)+H2 (g)→C2H6 (g)ΔH=−33 kcal C2H2 (g)+H2 (g)→C2H4 (g)ΔH= ? How can the enthalpy of Reaction III be calculated correctly? by subtracting the enthalpy of Reaction 1 from the enthalpy of Reaction 2 by adding the enthalpy of Reaction 1 and the enthalpy of Reaction 2 by first reversing Reaction 2 and then adding the enthalpy of Reaction 1 and the enthalpy of Reaction 2 by first multiplying the enthalpy of Reaction 2 by two and then finding the sum of the enthalpy of Reaction 1 and the enthalpy of Reaction 2. Study the reactions for the formation of compounds from their elements.

C (s)+O2 (g)→CO2 (g)ΔH=−394 kJ
H2 (g)+12O2 (g)→H2O (l)ΔH=−242 kJ
2C (s)+3H2 (g) →C2H6 (g) ΔH=−84 kJ

The combustion of C2H6 is shown by the following equation:

C2H6 (g)+72O2 (g) →2CO2 (g)+3H2O (l) ΔHc= ?
1,430 kJ
−1,430 kJ
286 kJ
−286 kJ
What is true about the spontaneity of a reaction?

When the products have less enthalpy than the reactants, the reaction is always spontaneous.
When the products have less enthalpy than the reactants, the reaction tends to be spontaneous.
When the products have more enthalpy than the reactants, the reaction is always spontaneous.
When the products have more enthalpy than the reactants, the reaction tends to be spontaneous.
Which statement is correct?

Natural processes happen spontaneously when they decrease the entropy of a system because entropy increase is counteracted by the flow of enthalpy from high temperatures to low temperatures.
Among solids, liquids, and gases, solids generally have the highest entropy because solid particles are the least mobile, and entropy is inversely related to mobility of particles.
Any change that increases the number of particles in a system increases entropy because it increases the randomness and disorder of the system.
Dissolving table salt (NaCl) in water leads to a decrease in entropy because salt particles, which are numerous individual crystals in solid form, become a homogenous solution in water. Examine the following reaction:

NH4Cl (s)→NH3 (g)+HCl (g)ΔH0=176 kJ
At 25 °C, this reaction has a ΔG0 of 91.1 kJ.

What is the ΔS0 of this reaction?

−0.285 kJ/K
0.896 kJ/K
−0.896 kJ/K
0.285 kJ/K
Study the reactions.

I. N2(g)+O2(g)→2NO(g)
II. CO(g)+12O2(g)→2CO2(g)
III. Na(s)+HCl(l)→2NaCl(aq)+12H2(g)
What factor would only affect the rate of the third reaction?

the pressure of the reactants
the concentration of the reactants
the temperature of the reactants
the surface area of the reactants
If the same amount of solid sodium (Na) is used in each reaction, which shape will increase the reaction rate the most?

strips of sodium
sodium powder
2 cm2 blocks of sodium
3 cm2 blocks of sodium
What effect does a catalyst have on the reaction rate and the products formed in a reaction?

The catalyst has no effect on the activation energy.
The catalyst has no effect on the amount of products formed at the end of the reaction.
The catalyst provides an alternate pathway with lower activation energy.
The catalyst increases the amount of products formed at the end of the reaction.
Study the chemical reaction.

A + B ⟶ C + D

A scientist studying this reaction states the reaction is first order with regard to A and zeroth order with regard to B.

What is the rate law for this reaction?

Rate = K [A][B]
Rate = K [A]2[B]
Rate = K [A]
Rate = K [B]
Study the reaction and read the statement.

2A + 3B + C → D + E

The rate constant for this reaction is 0.25.

The reaction is second order in A and first order in B and C.

What is the rate of the reaction if [A] is 0.4 M, [B] is 0.1 M and [C] is 0.2 M?

8.0 × 10–4
2.0 × 10–3
5.0 × 10–4
4.0 × 10–3