Which of the following would have an enthalpy of formation, oxHf$,$ of zero?

a$)H_{2}O(g)$

b$)M{g}^{2+}($aq$)$ c$)H_2{O}_{(1)}$

d$)O_{2(g)}$ e$)H^{+}(g)$

If the standard enthalpy of formation, oxHf$,$ for $A{g}_{(aq)}^{+}$ is $+105\mathrm{.}8k\frac{J}{m}ol$ and for $C{u}^{2+}(aq)$ is $+65\mathrm{.}7k\frac{J}{m}ol,$ what is the standard enthalpy of reaction, oxHr$,$ for:

$Cu(s)+2A{g}^{+}(aq)+2Ag(s)+C{u}^{2+}(aq)$

a$)-171\mathrm{.}5k\frac{J}{m}$olCub

d$)-73\mathrm{.}0k\frac{J}{m}$olCue

$25.$ Which statement about an activated complex is true?

a$)$ it is a stable substance

b$)$ it has higher potential energy than reactants or products

c$)$ it occurs only in endothermic reactions

d$)$ it always breaks down to form product molecules

$26.$ An endothermic reaction was found to have an activation energy of $100kJ.$ If this reaction is reversed the activation energy is only $20kJ.$ What is the value of oxH for the endothermic reaction? a$)-120kJb-80kJd$ e$)-200kJ$

$27.$ If a reaction rate increases by a factor of two when a particular reactant concentration is doubled, what is the order of the reaction with respect to that reactant?

a$)$ zero

b$)$ first

c$)$ second

d$)$ third

e$)$ fourth