General
Is water changing from gas to liquid endothermic or exothermic? Will the H be positive or negative?
Exothermic. The sign should be negative.
Calculate delta H of the following reaction:
H2 + Cl2 --> 2HCl
H-H: 436 kJ/mol
Cl-Cl: 243 kJ/mol
H-Cl: 431 kJ/mol
-183 kJ/mol
What are the three steps for any calorimetry problem?
1. q=mcat
2. q=-q
3. Stoichiometry to find H
What equation do you use for thermal equilibrium problems and what are the units of each part of the equation?
q=mcat
q= heat (J)
m= mass (g)
c = specific heat (J/gC)
at = change in temp (C)
The H for the following reaction is -810kJ. How many moles of A need to react to release -810kJ of heat?
A + B --> C
1 mole
When I add NaNO3 to water the beaker feels cold. Is the dissolution exothermic or endothermic? What is the sign of H?
This is endothermic. The sign should be positive.
Consider this reaction:
AB + C --> AC + B
If we know that the A-B bond is stronger than the A-C bond, is this an exothermic or endothermic reaction?
endothermic
For the following reaction I reaction, I react 0.158g of Mg and the temp rises from 25.6 to 32.8. If I have 101g of solution and the specific heat is 4.18, calculate the H.
Mg + 2HCl --> MgCl2 + H2
-468kJ
At thermal equilibrium, the temperature of two objects are:
a. different
b. the same
c. the larger object is higher than the smaller object
d. I don't care
b. the same
the heat gained by one object is equal to the heat lost by the other
The enthalpy for the following reaction is +456kJ. How many moles of B need to react to consume 200kJ of heat?
A + 2B --> C
0.877 mol
What has a higher specific heat: grass or pavement and how do you know?
Grass because it takes more energy to heat up to the same temperature as pavement.
Consider this reaction:
CD + F --> DF + C
If the C-D bond is much weaker than the D-F bond, is the H positive or negative?
Negative, this is exothermic.
Evaporating sweat cools the body because evaporation is endothermic.
H2O(l) --> H2O(g) H: +44.01kJ
What mass of water must evaporate to cool the body by 0.5 degrees Celsius?
Assume a body mass of 95kg and specific heat of the body is 4.0.
77g of water
If I add a 25g steel block that is initially 0 degrees Celsius (c = 0.49) into 25g of water that is initially at 40 degrees Celsius, what will the temperature be when it reaches thermal equilibrium?
35.8 degrees Celsius
The enthalpy of the following reaction is -5467kJ. How much heat is produced if 0.5g of A reacts with excess B. Assume that the molar mass of A is 45g/mol.
3A + 7B --> 12C
-20kJ
Draw the energy diagrams for and endothermic reaction and an exothermic reaction. HINT: energy is on the y axis and time is on the x axis.
Endo: products are higher in energy than reactants
Exo: products are lower in energy than reactants
Calculate the deltaH of the following reaction:
CH4 + 4Cl2 --> CCl4 + 4HCl
C-H: 414 kJ/mol
Cl-Cl:243 kJ/mol
C-Cl: 331 kJ/mol
H-Cl: 431 kJ/mol
-420 kJ
How many L of methane is needed to boil 1250g of water? Assume STP, the initial temp of water = 25 degrees, and c = 4.18.
CH4 + 2O2 --> CO2 + 2H2O H: -810. kJ
0.4837 mol
If an object has a higher specific heat, its temperature will change _________ when the same amount of energy is applied.
a. less
b. more
c. chemistry is the greatest subject
d. I have no idea what specific heat is but now that Jamie is telling me I will remember when I am taking my quiz
a. less
(or d)
You are taking your quiz and come across a problem that you have no idea where to start? What should you do first?
a. Panic
b. Skip the problem and take a 0
c. Write down what information you know and see what equations you can plug those numbers into
d. take the test to the professor, crumble it up and put it on her desk, leave the room and drop out of school
C.
PLEASE DO NOT DO ANY OF THE OTHER ONES
If the surroundings gains 100J of heat, how much heat did the system lose? Is this exothermic or endothermic
It lost 100J. That is an exothermic reaction.
Calculate deltaH of the reaction:
C2H4 + HBr --> C2H5Br
C=C: 615 kJ/mol
C-H: 414 kJ/mol
H-Br: 368 kJ/mol
C-Br: 276 kJ/mol
-54 kJ
I react 0.100g of B5H9 and the water temp increases by 1.93 degrees Celsius. Assume the total mass of the solution is 852.4g and specific heat is 4.18. Calculate H for the reaction.
2B5H9 + 12O2 --> 5B2O3 + 9H2O
-8680kJ
If you mix 20g of water at 100 degrees Celsius with 10g of water at 50 degrees Celsius, what will be the final temperature?
83 degrees Celsius
2Fe2O3 --> 4Fe + 3O2 H: +824.2kJ
The formation of 35g of O2 results in the absorption of how much heat?
3 x 10^2kJ