Unit 6: Heat Review

Endo or Exo

100

When heat is absorbed in a chemical reaction

What is endothermic reaction

200

heat + KClO₃ --> KCl + O₂

What is endothermic?

300

Does the graph represent and endothermic or exothermic reaction?

What is exothermic?

400

The image demonstrating an exothermic reaction.

What is B: energy is being released, the products have less energy than the reactants

500

This letter represents a negative enthalpy (amount of heat being released).

What is D?

Heating/Cooling Curves

100

At which number do the liquid and gas phase both exist?

What is 4?

200

Calculate the heat of vaporization if this heating curve was for 6.0 g of a sample.

28 J-15 J= 13 J

13 J / 6.0g = 2.2 J/g

300

The amount of heat needed to warm a 8.5 g ethanol sample from -100.0 °C to the gas phase.

-100.0 °C --> 78 °C (bp) + boiling

mc_lT + mH_v =q

(8.5g)(2.45 J/g°C)(178°C) + (8.5g)(841 J/g)=

11000 J

400

The amount of heat when 10.5 g ethanol sample cools from 0.0°C to -120.0°C

0.0°C --> -114°C + freezing + -114°C --> -120.0°C

mc_lT + m-H_f + mc_sT =q

(10.5g)(2.45 J/g°C)(-114°C-0.0°C) + (10.5g)(-109 J/g) + (10.5g)(1.70 J/g°C)(-120.0°C- -114°C) =

-4200 J

500

The amount of heat required when 20.5 g ethanol sample warms from -120.0°C to 120°C

-120.0°C --> -114°C + melting + -114°C --> 78°C + boiling + 78°C --> 120°C

mc_sT + mH_f + mc_lT + mH_v + mc_gT =q

(20.5g)(1.39 J/g°C)(-114°C- -120.0°C) + (20.5g)(109 J/g) + (20.5g)(2.45 J/g°C)(78°C - -114°C) + (20.5g)(841 J/g) + (20.5g)(1.70 J/g°C)(120.0°C-78°C) =

31000 J

Heat & Calorimetry

100

The heat capacity of aluminum is 0.900 J/g°C. How much energy is needed to raise the temperature of a 8.50 x 102 g block of aluminum from 22.8°C to 94.6°C?

q= (850.g)(0.900J/g°C)(94.6°C-22.8°C)

q=54900 J

200

How many grams of water can be heated from 20.0°C to 75°C using 12500.0 Joules?

(specific heat of water is 4.184 J/g°C)

12500.0 = (m)(4.184 J/g°C)(75-20.0)

m= 54 g

300

A coffee-cup calorimeter contains 150. g of water at 24.6 °C. A 110. g block of molybdenum metal is heated to 100.0°C and then placed in the water in the calorimeter. The contents of the calorimeter come to a temperature of 28.0°C. What is the specific heat capacity of the molybdenum metal if the specific heat capacity of water is assumed to be 4.184 J/g°C?

q_metal=-q_water

(110.g)(c_metal)(28.0-100.0)=-(150.g)(4.184 J/g°C)(28.0-24.6)

c_metal= 0.269 J/g°C

400

A 28.4 g sample of aluminum is heated to 39.4°C, then is placed in a calorimeter containing 50.0 g of water. Temperature of water increases from 21.00°C to 23.00°C. What is the specific heat of aluminum?

q_metal=-q_water

(28.4g)(c_metal)(23.00-39.4)=-(50.0g)(4.184 J/g°C)(23.00-21.00)

c_metal= 0.898 J/g°C

500

A 2.50 g sample of zinc is heated, then placed in a calorimeter containing 65.0 g of water. Temperature of water increases from 20.00°C to 22.50°C. The specific heat of zinc is 0.390 J/g°C. What was the initial temperature of the zinc metal sample?

q_metal=-q_water

(2.50g)(0.390 J/g°C)(22.50-T_i)=-(65.0g)(4.184 J/g°C)(22.50-20.00)

T_i= 720.°C

Miscellaneous

100

This color represents the energy pathway of a catalyzed reaction.

What is green?

200

This letter shows the E_a of the reaction:

What is B?

300

This letter shows the heat (delta H) of the reaction.

What is Letter D?

400

Something that causes atoms/molecules to move quicker and thus speeds up a chemical reaction.

What is temperature/heat?

500

A substance that increases the speed of a reaction by lowering the activation energy without being used up in the reaction.

What is a catalyst?