DAT stoichiometry/ thermal general chemistry

what is a characteristic of a combination reaction vs. a displacement reaction

-combination reaction: two elemental molecules come together (no oxidation state) -displacement rxn: one replaces the other

A. ∆T > 0 B. ∆G = 0 C. ∆G < 0 D. ∆G > 0 E. ∆S < 0 Neg (delta H) + neg delta S by plugging in to the equation Equals neg delta G is answer; easy!

Consider the following reaction at 298K: 2NH3 → 3H2 + N2 ∆H = -92,400 J/mol ∆S = 310 J/K Which of the following is true? t3

A researcher is running an experiment within a bomb calorimeter. The researcher noted that during the reaction process: pressure increased, entropy decreased, enthalpy increased, temperature increased, and heat energy remained constant. What type of reaction process was the researcher observing? A. Isenthalpic B. Isobaric C. Isentropic D. Adiabatic E. Isothermal

adiabatic process is one in which heat energy remains constant (∆q = 0).

Calculate the standard enthalpy change for the combustion of methane from the following data.6 CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) C(graphite) + 2H2(g) → CH4(g) ΔHo = 75 kJ/mol C(graphite) + O2(g) → CO2(g) ΔHo = -570 kJ/mol H2(g) + 1⁄2 O2(g) → H2O(l) ΔHo = -390 kJ/mol

given an equation just match and add E. -75 + (-570) + (-780)

Hydrogen gas and nitrogen gas react to produce ammonia. How many liters of ammonia can be produced from 2 liters of hydrogen gas and 2 liters of nitrogen gas at STP?

find LIMITNG REAGENT using liters Write out balanced equation; N2 + 3H2 → 2NH3 (ammonia vs ammonium--. Ammonia is shorter name so has the 3 vs 4) use each reactant to solve for product total (use rxn ratios) LR problem we would look for Mols but we can use Liters and Mol ratios A. 1.3

Which of the following would be the empirical formula of a compound that has 16 moles of oxygen and 56 moles of nitrogen?

find molecular mass on periodic table divide twice get ratio and find answer closest to it dont get too hung up if you get a decimal point multiply by 2 to get whole numbers 16/16 and 56/16 C. N7O2

In a reaction between 6g of oxygen gas, 4g of hydrogen gas, 5g of solid sulfur at standard pressure and temperature to make H2SO4 which is the limiting reagent? hydrogen oxygen sulfur

find mols of reactants; whichever one runs out first use reaction coefficients to divide all mols oxygen is needed 2x according to the coefficient in the rxn answer: oxygen

adiabatic

process is one in which heat energy remains constant

10 kJ of heat was applied to a 150 g sample of copper at 50°C. The specific heat of copper is 0.39 J·g-1·°C-1. What is the final temperature of the copper after the heat is applied in °C?

q = mCspecificT unit is "J" not KJ 10,000 J =( 150 ) (.39 ) (F-50) 10,000 / ( 150 ) (.39 ) +50 = Final

A volumetric flask weighs 185g when empty and 380g when filled with "liquid A" (density of 2 g•mL-1). If the flask is filled with 160g of "liquid B", what is the density of "liquid B" in g•mL-1?

we want density (not a gas problem) density = mass/volume 1. Use the info of liquid A to find volume of flask 2. density of B = 160/ found volume

?????? Water has a specific heat of 4.18J/g C while glass has a specific heat of 0.78 J/g C. If 40 J of heat is added to 1.00 g of each of these, which will experience the larger temperature increase?

what are we trying to cancel? look at units we can cancel the grams--> water: (4J/gC) (1gram)-->4J/C (40J)--flip-- (40J)(C/4J) glass: do the same here E glass

Actual yield must be determined by

what is given in the problem in grams "produced"

Chaqnge in Internal Energy formula

ΔE=w+q w= work q = heat

heat of formation formula

ΔHoreaction=ΔH(products)−H(Reactants) match equation multiply by coefficients if any

Consider the following reaction: c2H2 + 5/2 O2 --> 2 CO2 + H2O Hrxn = -1255.5 Kj/mol If the Hfomation of Co2 is -393 kj/mol and the Hformation of H2O is -241 kj/mol, what is the Hformation of acetylene, c2h2?

ΔHreaction=ΔH(products)−H(Reactants) -1250 = 2*400 - 250 1250 -800-250 = 200KJ H of reactants

At standard temperature and pressure, what volume of hydrogen will be produced when 6.5g of zinc is dissolved in hydrochloric acid, as shown in the reaction below? Zn(s) + 2HCl(aq) → ZCl2 (s) + H2(g)

"standard temp and press" 22.4L 1. find mols using Mw in periodic table 6.5g Zn (65 g/ 1mol) = .1 mols Zn 2. use reaction ratio .1 mol Zn (1mol H2/1mol Zn) (22.4L / 1mol) = 2.2 L

A sample of chromium oxide is 76.5% chromium by weight. What is the simplest formula of the oxide? t1 A. CrO3 B. CrO2 C. CrO D. Cr2O E. Cr2O3

(percent given / MW of ea. molecule) → divide answers by limiting number Cr = 76.5% subtract Find Percent of other 1-76.5 = 23.5--> O = 23.5% Cr = 76.5% / 52 9 (mw of Cr) = 1.4711... O = 23.5 % / 16 (mw of O) = 1.46875. Hence Cr:O :: 1.4711 ... : 1.46875... :: 1:1

The standard enthalpy of formation of liquid methanol is provided below, C(graphite) + 2H2(g) + 1⁄2O(g)2 → CH3(l)OH ΔHf = -239 kJ Which of the following would most likely be the value of the standard enthalpy of formation of gaseous methanol? A. -412 kJ B. -278 kJ C. -239 kJ D. -200 kJ

-converting from a liquid to a gas requires an input of energy -Therefore, we would expect a gas to have a more positive (less negative) ΔH than a liquid, as more energy is involved (ie. less energy is released). -Dont need to do math just find answer choice that is most pos -D. -200 kJ

If delta H is found to be positive, what can we conclude about the reaction? a spontaneous b non spontaneous c heat is absorbed d heat is released

-positive people absorb -negative people will release and vent

Calculate the heat of combustion of methane gas at 25celcius, use the table

-so the O2 can be left out (stable form on an element) -products - reactants (dont forget to include coefficients in the equation - I left out the table pic to allow for the example on how to solve

A given substance has a boiling point of 177oC, and a molar heat of condensation of -90 kJ/mol. What is the molar entropy of condensation of the substance? A. - 200 J/mol K B. - 24 J/mol K C. 133 J/mol K D. 283 J/mol K E. 339 J/mol K

1. Boiling point change to K units → T 2. KJ change to J/mol→ delta H (heat of condensation) 3. Plug in A. - 200 J/mol K

A sample of hydrated magnesium sulfate weighs 21.0 g: MgSO4 • xH2O It is placed inside of an oven until all of the water is vaporized, the anhydrous form weighs 12.0 g. What is the value of x in the hydrated salt? (MgSO4 MW = 120 g•mol-1. A. 3 B. 4 C. 5 D. 6 E. 7

1. Find grams of each component given (21g-12g) MgSO4 9g H2O 12g 2. find mols of each MgSO4 9g (1mol / 120 g) = .6 mol H2O 12g (1 mol/18g) = .07 mol (LR) 3. divide again by LR .6 mol /.07 = 5.2 (sort of) .07 mol (LR) /.07 = 1 were looking for of water--> = 5.2 answer; C. 5

The percent composition of an unknown element X in CH3X is 32 percent . Which of the following is element X? a. H b. F c Cl d Li e N

1. Subtract 100% -32% (uknown) = 68% (CH3) 2.Find molar mass of CH3 12+3 = 15 grams of CH3 3. divide: grams ch3 / percent ch3 (part g/ whole g%) 15 grams ch3/ .68 ch3 = 22grams total molecule 4. total grams - ch3 grams = uknown grams 22-15 = 7g uknown

Determine the molecular formula and calculate the percent composition of each element present in nicotine, which has an emperical formula of C5H7N and a molecular mass of 162 g/mol.

1. Use emperical formula to find mass of each atom C = 5*12 H= 7*1 N = 1*14 total mass = 81grams 2. actual mass given / theoretical mass = coefficient --> 2 3. multiply emperical formula by coefficient answer: C10H14N2

If 28g of Fe are reacted with 24g of S to produce FeS, what is the limiting reactant? How many grms of excess reactant are present in the vessel at the end of the reaction? Fe + S --> FeS (balanced)

1. find mols of each using MW in pt: 28g (1mol/ 56g) = .5 mol Fe 24g (1mol/ 32g) = 0.75 mol S 2. SUBTRACT .75-.5 =.25 EXCESs .25 mol* (32g/1mol S) = 8grams of S

What is the percent composition of chromium in K2Cr2O7 (potassium's molecular mass is 39g/mol, chromium's is 52 g/mol, and oxygen's is 16g/mol)?

2 *52g/com (the subscript comes up) find total mass = 2*39 + 2*52 + 7*16 = 294 2*52/294 X100 =35%

Describe the reaction below. PCl3(g) + Cl2(g) → PCl5(g) ; ΔHf = -87.9 kJ/mol A. spontaneous at all temperatures B. nonspontaneous at all temperatures C. ΔGrxn < 0 only at low temperatures D. spontaneous only at high temperatures E. ΔGrxn < 0 only at high temperatures

2 moles PCl + Cl on right → 1 mol on left (S is negative) ΔG = ΔH directly proportiona ; neg delta G means spontaneous watch out for negative people they can be spontaneous Answer C. ΔGrxn < 0 only at low temperatures

50 g of hydrogen reacts with 280 g of nitrogen to form ammonia. What is the theoretical yield of ammonia produced?

50g will run out faster = LR solve for products using the mols of hydrogen

5kg of calcium carbonate is left out in the sun for a while. A thermometer registers that the CaCo3 rose in temperature from 22C to 34C. How much heat did the compound absorb if the specific heat of calcium carbonate is 0.86 J / g*C? 520 5200 52KJ

52KJ specific heat uses J, grams, celcius not Kelvin

-use periodic table to find molar mass of both compounds given -set up a mol: mol ratio of both compounds to find the grams of "wanted"

>>>>how to find LR>>>>168 grams of calcium oxide produces 76g of ammonia; what is the percent yield?

Thermodynamic quantities

???

https://www.youtube.com/watch?v=liGCU9gaLcM&t=8s in this problem your given your reaction your coefficient will become your exponents--> then just solve for K (rate constant) according to the video

A rate law is an expression which relates that rate of a reaction to the rate constant and the concentrations of the reactants. A rate constant, kk, is a proportionality constant for a given reaction. The general rate law is usually expressed as: Rate=k[A]^s[B]^t

A. 3 B. 4 C. 5 D. 6 E. 7 SUBTRACT !! Find grams of each component given (21g-12g) anhydrous --> MgSO4 12g H2O 9g 1. find the mols of each (grams/ g/mol = mols) 3. Divide both by smallest number (limiting mols) → will give you X https://www.youtube.com/watch?v=t3A69QIlpwM C. 5 1. 9g / 18 (g•mol-1) = 0.5 mol of water The molar mass of water is 18 g•mol-1. 2. 0.12 / 120g = 0.10 mol of MgSO4 To find the mol of MgSO4, we use the anhydrous salt (only salt, no water) Finally, we divide by smaller number: 3. 0.5 water / 0.10 salt = 5 So the formula of the hydrated salt is: MgSO4 • 5 H2O

A sample of hydrated magnesium sulfate weighs 21.0 g: MgSO4 • xH2O It is placed inside of an oven until all of the water is vaporized, the anhydrous form weighs 12.0 g. What is the value of x in the hydrated salt? (MgSO4 MW = 120 g•mol-1.) t5

the problem is telling you the reaction is spontaneous -you can eliminate some of the answers H and S have to be positive for a reaction to be spontaneous (neg G)

A spontaneous reaction has the following coordinate diagram..

Theoretical yield

Actual // Theoretical

The ∆Hf for Br(g) is +193 kJ/mol. What is the "bond dissociation energy" of a Br-Br bond? t2 A. +193 kJ / mol B. -193 kJ / mol C. +386 kJ / mol D. -386 kJ / mol E. +96.5 kJ / mol

Br2(liquid) → 2 Br (g) (2) (193 KJ/mol) = 386 remember HONClBrIF (diatomics) Bond dissociation energies = always positive eliminate neg answers

Which of the following defines a reaction that is temperature-dependent? i positive H, positive S ii positive H, negative S iii negative H, positive S iv negative H, negative s

C i and iv G to be dependent of temperature will have to have H and S matching

Ammonia is formed according to the reaction below. A chemist mixes 21 grams of nitrogen gas and 18 grams of hydrogen gas in a 2.0 L vessel. How many grams of hydrogen gas will be consumed?6 N2(g) + 3H2(g) → 2NH3(g)

C. 4.5 grams Limiting reagent problem!!! (find mols of each) 1. Use molar ratio = 1 N2 is consumed for every 3 H2 2. Find mols of H2 used = 2.25 moles of H2 are consumed, 3. H2 consumed : 2.25 mole (created) * 2g/mole (MW)= 4.5g consumed

How many grams of oxygen are needed to completely react with 0.50 moles of C3H8 (58 g/mol)? A. 12 g B. 20 g C. 80 g D. 160 g E. 400 g

C. 80 g -Not a GMAR problem → stoichiometry needed -Write out combustion and balance (CH + O2--> co2 +H2O) -(0.5 mols C3h8) (molar ratio 5/1) (32 grams O2/ 1 mol ) → grams of O2 -Note: Mols and mols of diff atoms can touch , grams and grams cannot touch (dimen. analysis) (get this for youtube vid)

Which of the following molecules can be involved in hydrogen bond formation but cannot form hydrogen bonds with molecules of its own kind? A. C2H5OH B. HCOOH C. CH3OCH3 D. HFE. H3O+

C. CH3OCH3 ether's hydrogen atoms will not be involved in hydrogen bonding.

A. ΔS > 0 B. ΔS < 0 C. ΔG < 0 D. ΔH > 0 E. ΔS = 0 Count molecules on R → count on L 2: 1 ratio decreasing S "entropy"

Ca2+(aq) + SO4-2(aq) → CaSO4(s) Which of the following must be true for the above reaction? t3 A. ΔS > 0 B. ΔS < 0 C. ΔG < 0 D. ΔH > 0 E. ΔS = 0

A. 1.8KJ products -reactants

Calculate the enthalpy change for the following process:

Super easy match the given equation to data given L side to L side in data given It its flipped multiply by -1 A. -75 + 570 + 780 B. 75 + 570 + 780 C. -75 + (-570) + 780 D. 75 + (-570) + (-780) E. -75 + (-570) + (-780)

Calculate the standard enthalpy change for the combustion of methane from the following data.6 CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) C(graphite) + 2H2(g) → CH4(g) ΔHo = 75 kJ/mol C(graphite) + O2(g) → CO2(g) ΔHo = -570 kJ/mol H2(g) + 1⁄2 O2(g) → H2O(l) ΔHo = -390 kJ/mol A. -75 + 570 + 780 B. 75 + 570 + 780 C. -75 + (-570) + 780 D. 75 + (-570) + (-780) E. -75 + (-570) + (-780)

An exothermic reaction at equilibrium will proceed at a: A. slower rate while its Kc increases at higher temperatures. B. slower rate while its Kc decreases at higher temperatures. C. faster rate while its Kc increases at higher temperatures. D. faster rate while its Kc decreases at higher temperatures.

D. faster rate while its Kc decreases at higher temperatures. increasing the temperature will always make a faster rate Kc = CD// AB → reactants will be denominator making the ratio smaller = decreasing Kc

Consider the following chemical reactions. 2H2 + O2 → 2H2O H2O → H2O According to Hess' Law, what is the total enthalpy for the equation: t4 2H2O → 2H2 + O2

E. (-1)(-242) + (-2)(-286) "Hess Laww" matching!! Rxn 1 LEFT side matches RIGHT side of target equation → flip Rxn 2 has to be flipped and mult by coefficient of 2. (you have to do the same to the delta H)

What is the percent by mass of oxygen in sulfurous acid (H2SO3)?

Find O3; (16 x 3 = 48) Find total mass 48) is more than half of 82. D is the only answer with 58% (more than half)

All of the following statements are true of entropy EXCEPT for one. Which one is the EXCEPTION? t1 A. Entropy will increase as temperature increases B. Entropy is a measure of the disorder in a system C. A spontaneous reaction can produce an increase in entropy D. The entropy of a forward reaction is the same as the entropy of the reverse reaction E. The entropy of a gas vessel increases as volume increase

Forward rxn may have more or less "disorder" / entropy than the reverse rxn D. The entropy of a forward reaction is the same as the entropy of the reverse reaction (false)

What is the enthalpy of formation of N(g) in the following reaction? N2 (g) --> 2 N (g) Hrxn = 945.2KJ

Hrxn = Hproducts - Hreactants 945.2 = 2(Hproducts ) - (Hreactants)

18 grams

Molecular Weight of H2O

What are the coefficients that must be used to balance the combustion of butane: t3 C4H10 + O2 → CO2 + H2O

Multiply right and left sides multiply by denominator ONLY

Which of these changes represents a path function (non-state function)?7 A. Enthalpy B. Volume C. Work D. Mass E. Gibbs free energy

Path functions depend on the transition or change of the state. Heat and work are examples of path (non-state) functions. C. Work

A. Na+ (aq) + Cl- (aq) --> NaCl (aq) B. Na (s) + 1/2 Cl2 (g) --> NaCl (s) C. Na (g) + 1/2 Cl2 (g) --> NaCl (g) D. 2Na (s) + Cl2 (g) --> 2NaCl (s) E. 2 Na (g) + Cl2 (g) --> 2NaCl (s) Each ion should be in its natural periodic state Na naturally a solid Cl naturally a gas Your allowed to use half coeeficients (½ of Cl2 will equal 1 Cl)

The ΔH for which of the following reactions is the standard enthalpy of formation (ΔH°f) for sodium chloride? t5 A. Na+ (aq) + Cl- (aq) --> NaCl (aq) B. Na (s) + 1/2 Cl2 (g) --> NaCl (s) C. Na (g) + 1/2 Cl2 (g) --> NaCl (g) D. 2Na (s) + Cl2 (g) --> 2NaCl (s) E. 2 Na (g) + Cl2 (g) --> 2NaCl (s)

The following reaction was performed in water: H2SO4 + 2KOH → K2SO4 + 2H2O How many moles of K2SO4 are produced from 2.5 L of 0.3M KOH and 1 L of 0.3M H2SO4?7 A. 0.30 mol B. 0.38 mol C. 0.60 mol D. 0.75 mol E. 3.8 mol

Use Liters to get moles find LR>>> add tutor nites fir LR Their asking for moles of the excess molecule? → use molar ratios to find mols of K2SO4 LIMITING REAGENT PROBLEM -Liters are given instead of Grams (GMAR is not LMAR)

Internal Energy is defined as

We use the symbol ΔE to represent any changes in the internal energy of the system and account for these changes through work and heat ΔE=w+q

A. 1, 6.5, 4, 5 B. 2, 5, 8, 10 C. 2, 26, 8, 10 D. 2, 10, 10, 8 E. 2, 13, 8, 10 when you get an odd number balance the other side with a fraction - in this case you balance the left side with 5/2 Multiply right side and left side by ONLY denominator (to eliminate fractions) Solve each line moving downward https://www.google.com/search?q=balancing+chemical+reactions+with+fraction&oq=balancing+chemical+reactions+with+fraction&aqs=chrome..69i57j0i22i30l7.11030j0j4&sourceid=chrome&ie=UTF-8#kpvalbx=_SGGJYL-MHame0PEPhYWR-Ak22

What are the coefficients that must be used to balance the combustion of butane: t3 C4H10 + O2 → CO2 + H2O

Q. No. 2 Which of the following quantities is not a state function? Temperature Entropy Enthalpy Work

Work Explanation: Work done depends on the path taken. Heat depends on the path taken

In air bags, the reaction of sodium azide (NaN3, 65 g/mol) to form sodium and nitrogen gas is triggered by an electric current, thus expanding the air bag. If there are 65 grams of sodium azide in the air bag, how many mols of nitrogen gas are formed?

balance it; Write out formula nitrogen gas has a 2 bc diatomic!!! Dont write N3 write it out (move left to right in each row) g/mol go on top mw grams go at bottom use mol ratio to find what you want answer: B. 1.5 mols

Calculate the enthalpy change for the following process

change in enthalpy = products - reactants

Which of the following statements regarding an exothermic reaction must be true? a.spontaneous b.non spontaneous c.the products have more energy than reactants d.the energy of the ambient particles has increased

d.the energy of the ambient particles has increased a. and b. are wrong because you would need to know info about temp.(T) and enthalpy (S) on top of knowing its exothermic (-H)

What is the change in internal energy of an exothermic reaction at constant pressure, if 50 kJ of heat left the system and 20 kJ of work was done by the system in an expansion?

delta E = w+q -50 + 20 = -30 KJ

sublimination occurs quickly at room temperature

delta G will be negative bc "quickly" is spontaneous

A compound was found to contain 24.74% by weight potassium, 34.76% manganese, and 40.50% oxygen. Determine the empirical formula.

divide by atomic mass from periodic table use ratios to find integer numbers K : Mn : O = 0.63 : 0.63 : 2.53 = 1 : 1 : 4 KMnO4

Combustion analysis of a sample compound containing only C and H determines there was 18 g of C and 1 g of H in the sample. What is the empirical formula of this compound? A. C2H2 B. C3H2 C. CH3 D. C1.5H E. C2H3

divide by molecular mass on periodic table divide by smallest number DONT GET BOGGED DOWN BY DECIMALS assume .5 and move on 1.5 mol C and 1 mol H. Chemical formulas cannot contain decimals, so multiply each value by 2. B. C3H2

law of conservation of energy states...

energy is not created/ destroyed but transfered the energy lost from the reactants is gained by the sourrounding environment; meaning an increase in energy due to increase in temperature

A sample of white phosphorus was reacted with excess Cl2 gas to yield 68.75 grams of phosphorus trichloride. How many discrete P4 molecules were there in the sample?

given products molecules!! use avrogados 6x10^23 write the equation use given grams to find mols PCl3: Number of moles = (68.75 g Pcl3)/ [(31.0 + 35.5 x 3) g mol-1] pcl3 = 68.75/137.5 (around .5) mols of pcl3 use mol ratio of P4 and PCL 1 to 4 answer: A. [(69/138mol p4)/4 mol pcl3] (6.0 x 10^23)

How many grams of lead(II) sulfate (303 g/mol) are needed to react with sodium chromate (162 g/mol) in order to produce 0.162 kg of lead(II) chromate (323 g/mol)?

grams given will go at top grams/mol will go at bottom use formula Molar ratios

"heat left the system"

heat left is exothermic -q

What is the specific heat capacity of a piece of copper with a mass of 20.0 g that was heated to 24.58°C and then placed in a calorimeter that contained 50 g of water at 18.4°C? The final temperature of the water and copper was 20.4°C and the specific heat of water is 4.18 J/°C•g

https://www.chemteam.info/Thermochem/MixingMetal&Water-Probs1-15.html

What is the sum of the coeeficients when balanced: Mg3N2 + H2O --> Mg(OH)2 + NH3

key: you have to combine the 6 OH's and 6H's to balance and get 6 H2O's in the reactant side

The bond energy of N-H bond is 389Kj/mol, the bond energy of O=o bond is 498, and the bond enthalpy of the N==N (tripple) bond is 941. Given the following chemical reaction, what is the bond energy of the O-H bond? 4 Nh3 + 3O2 --> 2N2 + 6H2O Hrxn = -1266kJ

list all bonds broken (+) and bonds formed (-) set OH as X add all values together 4coefficient *(3 bonds) NH3 = 12 bonds 6coefficien * (2 bonds) H2O = 12 bonds [12*389 N-H + 3*498 O-O] - [2*941 N-N + 12*XO-H] OH= 450 KJ

What is the MAXIMUM amount of work that can be done by the following reaction at 30C if H = -125KJ and S=-200 J/K?

maximum amount of work use: G= H - TS G= -125 - (30C + 273) (-.2J) = -64.4 KJ

What is the molecular formula of a compound that contains 40.9% carbon, 4.58% hydrogen, and 54.52% oxygen by mass and has a molecular mass of 264g/mol (carbon's molar mass is 12g/mol, hydrogen's is 1g/mol, and oxygen's is 16 g/mol?

molecular formula = multiply given total molecular mass = 264 g find mols of each atom mols = (percent given)**(total molecular mass) / MW of atom C= .409*264/12 --> 9mol H= .0458*264/1--> 12mol O = .54*264/ 16--> 9mol answer: C9H12O9

The standard enthalpy of formation of liquid methanol is provided below, C(graphite) + 2H2(g) + 1⁄2O(g)2 → CH3(l)OH ΔHf = -239 kJ Which of the following would most likely be the value of the standard enthalpy of formation of gaseous methanol? A. -412 kJ B. -278 kJ C. -239 kJ D. -200 kJ

read the question what is it asking????? liquid form to gaseous D. -200 kJ liquid to a gas requires an input of energy Dont need to do math just find answer choice that is most pos

q = mCT

specific heat formula q = Joules of heat T = final - initial

Super easy match the given equation to data given L side to L side in data given If its flipped multiply by -1

standard enthalpy change

The ΔH for which of the following reactions is the standard enthalpy of formation (ΔH°f) for sodium chloride?

standard enthalpy of formation!!!! Each ion should be in its natural periodic state Na naturally a solid Cl naturally a gas Your allowed to use half coeeficients (½ of Cl2 will equal 1 Cl)

???? Calculate the heat of combustion of methane gas at 25celcius, use the table

the most stable form of an element will have a (heat of formation of 0) so the O2 can be left out -products - reactants (dont forget to include coefficients in the equation

If the total molecular mass changes what does it do to percent composition?

the percent of carbon will be lower where there is more "other stuff" (higher total molecular weight)

A. 0.5 mols, ammonium chloride. B. 0.25 mols, ammonium chloride. C. 0.5 mols, sodium hydroxide. D. 0.25 mols, sodium hydroxide. E. 1 mol, ammonium chloride Find MOLS!!! Of both reactants: use periodic table to add mw ----edit this with the info the tutor gave about finding LR>>>Smallest MOLS = LR, Limiting Reagents Excess = large amount - small amount

tutor ????? A chemist adds 26.5g of ammonium chloride to 10g of sodium hydroxide, which follows the reaction below. Assuming the reaction goes to completion, how much of which reactant is left in excess? t2 NH4Cl + NaOH → NH3 + H2O + NaCl