Unit 5: Thermochemistry Review

The potential energy diagram of a reaction is shown. Which statement below is correct relating to this reaction?

• #1 represents the enthalpy change for this exothermic reaction.

• #2 represents the enthalpy change for this endothermic reaction.

• #3 represents the enthalpy change for this endothermic reaction.

• #4 represents the enthalpy change for this exothermic reaction.

Tags

NGSS.HS-PS1-4

One of the ingredients of cement is quicklime, CaO. When cement is mixed with water the CaO reacts with the water as follows:

CaO_(s) + H₂O_(l) --> Ca(OH)_2(s) ∆H = - 65.3 kJ

Which one of the following statements concerning this reaction is true?

• this is an endothermic process

• as the mixture reacts the container gets warmer because heat is released to the surroundings

• as the mixture reacts the container gets colder because heat is absorbed from the surroundings

• heat is taken in from the surroundings during this reaction

• 65.3 kJ is required for each mole of CaO reacted

Tags

NGSS.HS-PS1-4

Examine the equation

N₂O_4(g) --> 2 NO_2(g) ∆H = + 57.93 kJ

An alternate way to write this equation is:

• N₂O_4(g) --> 2 NO_2(g) + 57.93 kJ

• N₂O_4(g) + 57.93 kJ --> 2 NO_2(g)

• N₂O₄ + 57.93 kJ --> NO_2(g)

• N₂O_4(g) --> NO_2(g) + 57.93 kJ

• 2 NO_2(g) + 57.93 kJ --> N₂O_4(g)

Tags

NGSS.HS-PS1-4

For the formula:
 Q= m c ∆T
The  units for specific heat are:

• g /J C
• °C/g J
• kJ/g
• J/g°C

A sample of iron receives 50.J of heat energy that raises the temperature of the iron 25.0°C. If iron has a specific heat of 0.10 J/g°C, what is the mass of the iron sample?

• 25g

• 30g

• 20g

• 50g

How much heat (in joules) is needed to raise the temperature of 355 g of ethanol (c = 2.4 J/g^oC) by 63^oC?

• 54,000 J

• 94,000 J

• 22,000 J

• 852 J

Tags

NGSS.HS-PS3-4

What mass of iron (c = 0.11 cal/g^oC) would need 875 cal of energy in order to raise its temperature by 3.5^oC?

• 2300 g

• 340 g

• 28 g

• 28,000 g

Tags

NGSS.HS-PS3-1

NGSS.HS-PS3-4

Water has a specific heat of 4184 J/KgºC.  Wood has a specific heat of 1760 J/KgºC.  What material needs more energy to raise the temperature 1ºC

• Wood
• Water
• Both are the same

Tags

NGSS.HS-PS3-2

Copper, Stainless Steel, Carbon Steel, and Zinc started with the same initial temperature and were all heated using the same amount of thermal energy. What material would be the coolest after being heated?

• Copper

• Carbon Steel

• Zinc

• Stainless Steel

Tags

NGSS.HS-PS3-4

What is the specific heat of an alloy if 4210 joules are required to raise the temperature of a 30 g sample by 180°C?

• 0.78 J/g°C

• 0.25 J/g°C

• 1.78 J/g°C

• 2.34 J/g°C

Tags

NGSS.HS-PS3-4