Question

Help

Answer 1

CH4 & 2o2 = reactants
CO2 & 2H2O = products

Answer 2

perfect

Answer 3

How do an endothermic reaction and an exothermic reaction differ?

An endothermic reaction means that it's happening inside and an exothermic reaction means it is happening outside.

Answer 4

that's actually not quite true, exothermic vs endothermic is defined by the energy difference between reactants/products

Answer 5

An exothermic reaction is a chemical reaction that releases more energy than it absorbs. An endothermic reaction is a chemical reaction that absorbs more energy than it releases.

Answer 6

exo = releases energy, products have lower energy than reactants
endo = absorbs energy, products have higher energy than reactants

Answer 7

yeah, that's about right

Answer 8

egg would be endo?

Answer 9

yes

Answer 10

photosynthesis = ex
burning a candle= endo

Answer 11

photosynthesis is actually endothermic (ngl had to look this one up myself)

burning something is almost always exothermic

Answer 12

using an instant cold pack- exo
using a chemical hand-warmer-exo
car engine-endo

Answer 13

combustion (which is involved in the car engine) would be exothermic

cold pack - it absorbs heat from the environment so endothermic
hand-warmer would be the opposite of a cold pack, it gives off heat so exothermic

Answer 14

In the space below, draw a potential energy diagram for an endothermic reaction and a second potential energy diagram for an exothermic reaction. Give each graph a title, and label the reactants and products on each graph.

Answer 15

This woukld basically just be something like what you posted right?

Answer 16

This?

Answer 17

yes

Answer 18

yes no yes for the first one

Answer 19

keep in mind we're just talking about matter for the first row

Answer 20

isolated system does not allow either matter or energy so isolated would be no for first row

Answer 21

so yes yes no

Answer 22

or yes no no

Answer 23

YNN

Answer 24

what about row 2?

Answer 25

For energy it needs to be

Yes Yes yes

Answer 26

keep in mind an isolated system allows neither energy nor matter

Answer 27

Yes yes no :p

Answer 28

that's correct

Answer 29

Fill in the blanks in the following paragraph to correctly identify the signs associated with heat and work.
When a system is heated, heat is _______________ by the system. The amount of heat added is given a _______________ sign. When a system is cooled, heat is _______________ by the system. The amount of heat is given a _______________ sign. If a gas expands, it must push the surrounding atmosphere away. Thus, work is done _______________ the system and is given a _______________ sign. If a gas is compressed, then work is done _______________ the system. This work is given a _______________ sign.

Answer 30

thoughts so far?

Answer 31

um does it have to do with exothermic and endothermic

Answer 32

or expanded or extracted

Answer 33

for the first blank they're probably looking for something like "absorbed"

Answer 34

what about the second blank? positive or negative?

Answer 35

positive

Answer 36

actually neg.

Answer 37

you had it right the first time, heat absorbed gets a + sign

Answer 38

third blank is opposite of absorbed, so released, fourth is the opposite of positive, so negative

Answer 39

for "work done by system" do you remember if the sign is + or -?

Answer 40

positive but work done on the the system is neg

Answer 41

the gas is expanding so we say the work is done (by) the system (since we are looking from the perspective of the system, not the person doing work on it)

so 5th blank is "by" and 6th is positive

Answer 42

last two blanks are just the opposite of those two blanks, so "on" the system and negative sign

Answer 43

an then work done "on:

Answer 44

Yup that's what I was going to say

Answer 45

What is the change in internal energy if 50 J of heat are released from a system, and the system does 80 J of work on its surroundings?

Answer 46

the sign convention can be tricky, but if heat is being released what's the sign on heat, and if the system is doing work what's the sign on work?

Answer 47

the sign convention can be tricky, but if heat is being released what's the sign on heat= pos
if the system is doing work what's the sign on work= neg

Answer 48

heat is being released from the system, so from the system's perspective it's losing heat

work done (by) system is positive

so Q = neg, Work = positive

so if U = Q - W, U = ?

Answer 49

-50-80?

Answer 50

awesome, so -130J

Answer 51

a. Fill in the blanks in the following paragraph to correctly identify four principles of the second law of thermodynamics.

Heat naturally flows from an object that has a _______________ temperature to an object that has a _______________ temperature. Heat can be made to flow in the reverse direction if _______________ is done. A machine can never have an efficiency of _______________. This means that heat energy can never be fully converted into _______________ energy.

Answer 52

high temp to low temp?

Answer 53

yes

for the third blank, any ideas? what has to be done to make heat flow from low to high temp?

Answer 54

work

Answer 55

awesome

any ideas for the efficiency question?

Answer 56

um energy?

Answer 57

efficiency is usually given as a percentage, what percentage efficiency would be impossible according to the laws of thermodynamics?

Answer 58

100

Answer 59

good, so 100 percent goes into the blank

the last blank I'm actually not 100% sure but a good hunch would be "mechanical" :S

Answer 60

oh okay, i was leaning towards work but I am just guessing so I will do with mechanical

Answer 61

yeah I just double checked and it seems like it would be mechanical since work isn't classified as a type of energy

Answer 62

perfect

Answer 63

Describe entropy. What is the natural tendency of the entropy of a system?

Entropy is an important concept in physics that uses microscopic aspects to describe the thermodynamics of the systems of molecules. The natural tendency of the entropy of a system is to increase over time.

Answer 64

good start, probably should mention that entropy is the number of states/configurations a system can have

Answer 65

Entropy is an important concept in physics that uses microscopic aspects to describe the thermodynamics of the systems of molecules. It is also the number of the variations of states and/or configurations a system can have. The natural tendency of the entropy of a system is to increase over time.

Answer 66

good

Answer 67

How does a heat engine differ from a heat pump?

Answer 68

Heat Engine is the system that converts the Heat energy into mechanical work. while Heat pump converts the work into heat. Heat Engine is the system that converts the Heat energy into mechanical work.

Answer 69

good (make sure you delete that last sentence since you repeated yourself)

Answer 70

Im gonna open a new thread this is getting long

Answer 71

sure