Abeka New Chemistry Test 4

0.2331 J

A 25.0 g cube of silver with a temp of 95.0 C was placed in a calorimeter with 80.0 g of water at a a temp of 25.0 C. The temp of the water rose to 26.2 C from the data, It was calculated that the water gained 401 J of heat. What is the specific heat of silver? -Qag = Q water = 401 J Triangle T = 26.2 - 95.0 = -68.8C C ag = Q ag/M Triangle T = -401 J/ 25.0(-68.8 C) = 0.2331

barometer

A device used to measure heat is a

increases

As temperature increases, the vapor pressure of a substance ___________?

-34.3 kJ; spontaneous

Calculate Triangle G for the following reaction and tell whether it is spontaneous at 298.15 K. N2(g) + 3 H2 (g) -----> 2 NH3 (g) Triangle H = -91.8 kJ, Triangle S = -192.8 J/K Traingle S = (-192.8)( 1/1,000) = =0.1928 kJ/K Triangle G = Triangle H - T Triangle S = -91.8 - (298.25)(-0.1928) =-34.31

H

Enthalpy

S

Entropy

Q

heat

negative

if a reaction is exothermic, then triangle H will be __________

Yes; neither pressure nor volume is relatively constant

if the following reaction occurs in the laboratory at atmospheric pressure, will triangle H approximately equal triangle E ? Why or Why not? HCI(aq) + NaOH(aq)_--------> H^2O(I)+ NaCI(aq)

liquid water freezing

in which of the following processes is triangle S expected to be negative?

triple

the temperature and pressure at which the solid, liquid, and gas phases of a substance are in equilibrium is called the ______point

chemical thermodynamics

what area of chemistry deals with applying thermodynamic principles to energy changes in chemical reactions?

endothermic (reaction)

what general term describes a reaction that absorbs heat?

entropy

what is a measure of the disorder or randomness of a system's atoms and particles?

changes in internal energy and independent of the path taken

what is the BEST reason that internal energy is considered a state function?

critical point

what is the point on a phase diagram above which the distinction between liquid and gas disappears

standard state

what term refers to a substance's normal physical state at 100kPa and a specified temperature?

0 J

what value of enthalpy is assigned to an element in standard state?

triangleG>0

Which of the following indicates that a process as constant temperatures and pressure is NOT spontaneous?

First

The law stating that energy gained or lost by the system equals the energy lost or gained by the surroundings is the ________ law of thermodynamics.

2803 kJ

What is Triangle H (power of 0) for the following reaction? 6 CO2 (g) + 6 H2 O (I) ----> C6 H12 O6 (s) + 6 O2(g) Triangle F H (power of 0) [CO2(g)] = -393.5 kJ/mol Triangle F H (power of 0) [H2O(I)] = -285.8 kJ/mole Triangle F H (power of 0)[C6 H12 O6 (s)] = 1273.3 kJ/mole Figuring it out would be as follows: Triangle H (power of 0) = Triangle F H (power of 0) (Products) - Triangle F H (power of 0) (Reactants) = [1 mole(-1273.3 kK/mol) + (6 mol)(0 kJ/mol)] *Cross cancelling the mols out and solving = 2802.5 (round up)

sublimation

What is a change of substance from a solid directly into a gas?

phase diagram

What is a graph that shows the state of a substance at different pressures and temoeratures.

enthalpy of fusion

What is the energy per unit mass required to melt a substance at its melting point?

boiling point

What is the temperature at which a liquid's vapor pressure equals the total pressure of all gases present?

enthalpy

What quantity equals the internal energy plus the product of pressure and volume?

specific heat

What term refers to the heat required to cause a unit rise in the temperature of a unit mass of a substance?

second

Which law of thermodynamics predicts that processes with a positive change in entropy tend to be spontaneous?

third

Which law of thermodynamics states that it is absolutely impossible to cool a system to absolute zero in a finite time?

Hess's law

Which law states that when a series of reactions occurs, the enthalpy of the net reaction equals the sum of the individual reactions' enthalpies?

Essay Answer: a bomb calorimeter measures heat by measuring temp. The heat measured by a bomb calorimeter is equal to Triangle E. A bomb calorimeter cannot directly measure Triangle H. As described by the gas laws, the pressure in a bomb calorimeter changes as temp changes and as gases are produced or consumed by the reaction (changing the mole amount of gas present). A bomb calorimeter will be more accurate for measuring the heat of combustion reaction.

Essay Question: a bomb calorimeter van be used to measure Triangle E of physical or chemical processes. Because of its sealed pressure vessel, the volume of a bomb calorimeter is constant (Triangle V = 0), but the pressure is not necessarily constant. A constant pressure colorimeter is open to the atmosphere and the pressure remains constant (Triangle P=0) Use the equation W=P Triangle V to explain why a bomb calorimeter measures Triangle E instead of Triangle H. Will a bomb calorimeter or constant pressure calorimeter be more accurate for measuring heat of combustion reaction that produces a large amount of gas. Explain your choice.

G

Gibbs free energy

259 kJ

How much heat is absorbed when 30.0 g. of ammonium chloride reacts according to the following thermochemical equation? (M NH4 CL = 53.49 g/mol) NH4 Cl (s) + H2 O (I) ----> HCL(g) + NH3 (g) 30.0 g NH4 Cl/53.49 g/mol NH4 Cl = 0.5608 mol NH4 Cl (462.0 kJ/ 1 mol NH4 Cl)(o.5608 mol NH4 Cl) = 259.1

68,400 or 68.4 J

How much heat is needed to convert 30.0 g of water at the boiling point (100.0 C) into steam at 110.0 C. Triangle vap H = 2260 J/g, c steam = 2.08 J/g.C Triangle vap = M Triangle vap H Q vap = (30.0g)(2260 J/g) = 67,800 J Triangle T steam = 110. C - 100.C = 10.0 C Q stream = C stream M Triangle T stream = Q Stream = (2.08)(30.0)(10.0) = 624 J 67,800 + 624 = 68,424 = 68,400 or 68.4

liquid water; its energy is increased by the enthalpy of vaporization

If a sample of liquid water at 0 degree C have the same mass, which has more internal energy? Why?

product

In an exothermic reaction, heat can be considered a _______________.

238 J

In an experiment , 475 J of heat was added to a gas piston assembly as the piston did 237 J of work on the surroundings. What is the change in internal energy for this system? Formula is Triangle E = Q + W = 475 J + (-237 J) = 238 J