reaction types
What type of reaction occurs when two or more substances combine to form one product?
What is a combination reaction?
A reaction that releases heat to the surroundings is called what?
What is an exothermic reaction?
What equation is commonly used to calculate heat transferred when you know mass, specific heat, and temperature change?
q = mcΔT
What is the difference between the system and the surroundings?
The system is what we are focusing on, while the surroundings are everything else that could be affected by a change in the system.
Is enthalpy (H) a state function or a path function?
State function
In a single-displacement reaction, a reaction occurs when the neutral metal is ______ on the activity series than the metal ion it is trying to replace
What is higher?
A reaction that absorbs heat from the surroundings is called what?
What is an endothermic reaction?
In a coffee-cup calorimeter, is the process generally considered to occur at constant pressure or constant volume?
Constant pressure
According to the First Law of Thermodynamics, can energy be created or destroyed?
no.
Energy can only be transferred as heat and/or work.
When bonds are broken, is energy absorbed or released?
Energy is absorbed.
Determine whether a reaction occurs:
Zn(s) + Cu²⁺(aq) → ?
Given that Zn is above Cu on the activity series.
Yes, a reaction occurs.
A reaction has:
q = −450 J
Is the reaction exothermic or endothermic?
Exothermic
The negative q means the system released heat.
How much heat is required to heat 50.0 g of water from 20.0°C to 30.0°C?
Specific heat of water:
4.184 J/g°C
q = mcΔT
q = (50.0)(4.184)(30.0 − 20.0)
q = (50.0)(4.184)(10.0)
q = 2092 J = 2.092 kJ
A system absorbs 350 J of heat and does 200 J of work on the surroundings.
Calculate ΔE.
q = +350 J
w = −200 J
ΔE = 350 − 200
ΔE = +150 J
A reaction has:
q = −325 J
and
w = +125 J
Calculate ΔE.
ΔE = q + w
ΔE = −325 + 125
ΔE = −200 J
Which reaction type is represented?
2H₂O₂ → 2H₂O + O₂
Decomposition
A reaction absorbs 725 J of heat and does 125 J of work on the surroundings.
ΔE = q + w
q = +725 J
w = −125 J
ΔE = 725 + (−125)
ΔE = +600 J
A 100.0 g aluminum sample is heated from 25.0°C to 75.0°C.
The specific heat of Al is 0.900 J/g°C.
Calculate q.
q = mcΔT
q = (100.0)(0.900)(75.0 − 25.0)
q = (100.0)(0.900)(50.0)
q = 4500 J = 4.50 kJ
A gas expands from 2.0 L to 7.0 L against a constant external pressure of 1.0 atm.
Calculate the work.
Use: w = −PΔV and 1 L·atm = 101.325 J
ΔV = 7.0 − 2.0 = 5.0 L
w = −(1.0 atm)(5.0 L)
w = −5.0 L·atm
Convert:
−5.0 × 101.325 =
w ≈ −507 J
A 200.0 g copper sample is heated from 20.0°C to 80.0°C.
Copper's specific heat is 0.387 J/g°C.
How much heat is absorbed?
q = mcΔT
q = (200.0)(0.387)(80.0 − 20.0)
q = (200.0)(0.387)(60.0)
q = 4644 J = 4.64 kJ
Determine whether a reaction occurs:
Ni(s) + Na⁺(aq) → ?
Na is above Ni on the activity series.
No reaction
The Ni cannot displace Na⁺ because Ni is less reactive.
A system transfers 870 J of heat to the surroundings and does 420 J of work on the surroundings. Calculate E.
q = −870 J
w = −420 J
ΔE = q + w
ΔE = −870 − 420
ΔE = −1290 J
A 75.0 g sample of water absorbs 2.50 kJ of heat. Its initial temperature is 22.0°C.
What is its final temperature?
Use:
c = 4.184 J/g°C
Convert:
2.50 kJ = 2500 J
2500 = (75.0)(4.184)(ΔT)
ΔT = 2500 / 313.8
ΔT = 7.97°C
Final temperature:
22.0 + 7.97 =
29.97°C ≈ 30.0°C
A system absorbs 1.20 kJ of heat while doing 0.850 kJ of work on the surroundings.
Calculate ΔE in Joules.
q = +1.20 kJ
w = −0.850 kJ
ΔE = q + w
ΔE = 1.20 − 0.850
ΔE = 0.350 kJ
ΔE = +350 J
A reaction releases 5.00 kJ of heat while the system has 1.25 kJ of work done on it by the surroundings.
What is ΔE?
Releases heat:
q = −5.00 kJ
Work done on the system:
w = +1.25 kJ
ΔE = q + w
ΔE = −5.00 + 1.25
ΔE = −3.75 kJ