Name: Alma Aassaini 6. Dental cavities result when acidSubstance (H (aq) eats aw

Question

Name: Alma Aassaini 6. Dental cavities result when acidSubstance (H (aq) eats away tooth enamel (Ca5P3013H(s)) according to the balanced equation So [kJ/mol [JI(mol-K)] Ca5P3013H(s) 6760 390 H (aq) Ca2+ (aq) PO43-(aq) H20(0) 0 -542 53 -1,277 -222 -286 70 Ca5P3O13H(s) + H+(aq)- 5 Ca(a)3 PO4)o POA (a0)+0 H200 a. [6 points] Using data in the table, calculate AGo of the reaction at 310 K (body tem- perature) under standard state. -30 oo b. 3 points] Explain why the reaction happens spontaneously on the surface of teeth even though its value ofG" > 0 at 310 K. becunse according tote proeluchs in te rcachon, teit an more pre curt side, 4

Explanation / Answer

a)

dG = dH - T*dS

T = 310K, then

dH = 5*-542 + 3*-1277 + -286 - (-6760 + 0) = -67 kJ/mol

dS = 5*-53 + 3*-222 + 70 - (390 + 0) = -1251J/molK

dG = -67*1000 - 310 * -1251

dG = 320810 J/mol

dG = 320.8 kJ/mol

b)

note that this vlaue does NOT accounts for concentrations

this is STANDARD conditions

which implies

dG = dG° + RT*ln(Q)

note that if dG < 0, and dG° > 0, then

RT*ln(Q) must be negative

Q = quotien between concentrations

then

dG = (positive) + (negativE)

overall dG vlaue is negative, due to concentration

this will icnrease if H+ is high, i.e. low pH due to sweet/candy

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