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# Homework 30


## 1.35

A household receives a $125 electricity bill. The cost of electricity is$0.150 /kWh. How much energy, in joules (J), did the household use?

Solution:

Step 1: You must first multiply the total cost of the bill ($125) by 1 kWh and then divide that answer by the cost of each kW ($0.150 kWh). You should end up with an equation that looks like this:

$(125)\times \dfrac{1\;kWh}{0.150\;kWh}$

Step 2: Once you do this math, then you should receive the answer of 833.33 kWh. This is the number of kWh used during the billing cycle.

Step 3: Next, you will then take your solution found during step 1 and multiply it by $$\frac{1}{2.78\times 10^{-7}}$$ in order to convert kWh to kWh/J. You should have the equation:

$(833.33)\times \dfrac{1}{2.78\cdot 10^{-7}}$

Step 4: After completing step 3, you should receive an answer of $3.0 \times 10^{9} J$

Step 5: YOU ARE FINISHED!

## 2.45

Classify each substance as a pure substance or a mixture. If it is a pure substance, classify it as an element or compound. If it is a mixture, classify it as homogenous or heterogeneous.

1. tears
2. lithium hydroxide
3. gold
4. bowl of chili

Solution:

1. homogeneous mixture
2. pure compound
3. pure element
4. heterogeneous mixture

Step 1: You must know the difference between a:

• pure substance - A substance that is made up of only one type of atom or molecule.
• mixture - A material system made up of two or more different substances that are mixed but not combined together chemically.

Step 2: You must know the difference between:

• element - Cannot be broken down into simpler substances.
• compound - Substance formed when two or more chemical elements are bonded together chemically and can be broken down into simpler substances.
• homogeneous - Mixture that has a uniform composition and properties throughout (cannot see ingredients)
• heterogeneous - Mixture that remains physically separated throughout (can see ingredients)

Step 3: Label either pure substance or mixture

Step 4: Label each pure substance as either an element or compound and each mixture as either homogeneous or heterogeneous.

Step 5: YOU ARE FINISHED!

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