Vocabulary that Matters
Calculations
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Review
100
heat can be described as
What is the form of energy that is transferred between systems or objects with different temperatures?
100
The specific heat of lead metal, Pb, is 0.127 J/(g x °C). How many joules of heat would be required to raise the temperature of a 5.00 g sample from 25°C to 35°C?
What is C.) 6.4
The equation q = (m x c x ΔT) is needed to solve this problem. Substitute the given information to solve for q. q = (5.00 g)(0.127 J/(g x °C))( 35°C - 25°C) = 6.4 J
100
What is Hess's Law formula and what does it mean?
the net change in enthalpy of the overall reaction is equal to the sum of the changes in enthalpy for each intermediate transformation
100
The slow rate of a particular chemical reaction might be attributed to which of the following? A) a low activation energy B) a high activation energy C) the presence of a catalyst D) the temperature is high E) the concentration of the reactants are high
B—Slow reactions have high activation energies. High activation energies are often attributed to strong bonds within the reactant molecules. All the other choices give faster rates.
200
a measure of the average kinetic energy (KE) of an object's particles.
What is Temperature
200
The following is a list of specific heat capacities for a few metals. Ccopper=0.385 Ciron=0.444 Csilver=0.240 Caluminum=0.900
A 50g sample of an unknown metal is heated with 800 joules. If the temperature of the metal increases by 41.6oC, what is the identity of the unknown metal?
Copper
200
Describe to me how a caliometer works.
What is Calorimeter, device for measuring the heat developed during a mechanical, electrical, or chemical reaction, and for calculating the heat capacity of materials.
200
The energy difference between the reactants and the transition state is A) the free energy B) the heat of reaction C) the activation energy D) the kinetic energy E) the reaction energy
C—This is the definition of the activation energy.
300
the sum of all the KE of the molecules of a material. Directly related to mass, Q = mc delta T
What is Thermal energy
300
How much heat does it take to heat 100g ice at 0C to boiling point?
Cice= 2.1 J/goC
Cwater= 4.2 J/goC
ΔHvap= 2260 J/g
ΔHfus=334 J/g
75.4 kJ
300
How much heat is needed to raise 5 grams of aluminum by 20oC?
Caluminum=0.900Jg⋅oC.
90J
300
CsF is an example of this
What is a compound?
400
On the Celsius temperature scale, water freezes at ____° and boils at ____°.
0 and 100
400
The specific heat capacity of an unknown liquid is 0.32Jkg⋅K. The density of the liquid is 0.0321gmL If a chemist applies 243 J of heat to 300 mL of this liquid starting at 27.1∘C, what is the final temperature?
78882∘C
300mL×0.0321g1mL=9.63g
Now we will examine the relationship between heat and specific heat capacity:
Q=cmΔT
Where Q is heat in Joules, c is the specific heat capacity, m is the mass and ΔT is the change in temperature. We can rearrange this
ΔT=Qcm
ΔT=243J0.32J⋅kg−1⋅K−10.00963kg=78855K
If we begin at 27.1∘C, we will end at 78882∘C
400
What will happen to the rate of an exothermic reaction if the temperature is increased?
It will increase
400
This reaction could be classified in this way
2Na + 2H2O --> 2NaOH + H2
What is a single replacement reaction?
500
Describe a situation in which ice is endothermic and situation where it is exothermic.
Points awarded based on individual answers
500
If the decomposition of 2 moles of gaseous HCl into 1 mole each of gaseous H2 and gaseous Cl2 at 25∘C absorbs 185kJ of heat energy, then what is the standard heat of formation of HCl in kilojoules per mole?
−92.5kJmol
From the question stem, we are told that the breakdown of 2 moles of gaseous HCl requires an absorption of 185kJ of energy. For simplification, we can write out the reaction as:
ΔHrxn=+185.0kJ
By definition, the heat of formation of a compound is the enthalpy change that occurs for the formation (ΔHf) of that compound from its elements in their standard state. Since H2 and Cl2 are in their standard state, we know that they have a heat of formation of zero, thus simplifying the calculation. Thus, if we reverse the above reaction, we see that:
ΔHrxn=−185.0kJ
Notice that by reversing the reaction, we are also reversing the sign for the enthalpy of the reaction. Now, to calculate the ΔHf of HCl as kilojoules per mole, we need to multiply the reaction by one-half to obtain:
ΔHf(HCl)=−92.5kJmol
500
Why is the importance of fixed energy important to our calculations in thermodynamics?
because energy cannot be created or destroyed and thus it flows from one to another and as such we can measure how it increases and decreases.
.....sorry forgot the what is.
500
The table below gives the initial concentrations and rate for three experiments.
[CO]i (M) [Cl2]i (M) Initial Rate (M-1s-1)
0.25 0.40 0.996
0.25 0.80 1.97
0.50 0.80 3.94
The reaction is CO(g) + Cl2(g) → COCl2(g). What is the rate law for this reaction?
Beginning with the generic rate law: Rate = k[CO]m[Cl2]n, it is necessary to determine the values of m and n (the orders). Comparing Experiments 2 and 3, the rate doubles when the concentration of CO is doubled. This direct change means the reaction is first order with respect to CO. Comparing Experiments 1 and 3, the rate doubles when the concentration of Cl2 is doubled. Again, this direct change means the reaction is first order. This gives: Rate = k[CO]1[Cl2]1 = k[CO][Cl2].