I have a lot of homework questions i don’t get some of them. Please help me with them:
1. Low-density polyethylene is a plastic that can be stretched somewhat without breaking it. Why is this property useful for disposable shopping bags?
2. What are two physical changes that cooling a hot substance may result in? (I wrote liquids and solids, but I have no idea if it is right or wrong)
3. Why will water form droplets on a smooth surface, such as a counter top?
4. Metal foams are 75 to 95 percent air. What effect does this have on the density of metal foam compared to solid metal?
5. If water freezes inside of a building’s water pipes, the pipes may burst. Explain why this happens.
6. Consider a homogeneous mixture, such as a salt solution, anda heterogeneous mixture, such as rice and pebbles. Suggest and compare how you could separate the substances within each type of mixture.
YOU DO NOT HAVE TO ANSWER ALL QUESTIONS!!!!!!!!!!
Thank you soooooo much!!! 
1. elastic property – important to allow plastic bags to withstand heavier products and stretch to fit products.
2. Change in volume, change in state (solid – liquid, liquid – gas), change in temperature (no points for that answer lol). Think of a physical change as something that can be easily reversed. For example, you freeze water it becomes ice, you can then melt the ice to become water (it has changed its state). On the other hand a chemical change is a change in the actual product that can not be reversed. For example, baking a cake, you start of with a whole lot of ingredients then once they are mixed and baked to make a cake you can not reverse the process to get all the ingredients again. (Hope this makes these types of questions a little easier to understand).
3. This is a result of intermolecular forces – attractions between molecules. Water has a strong intermolecular for therefore drops will form on a smooth surface to increase the surface area of the water. (not really the best answer to this question I am sorry but you must have learnt this go back over notes and look for keywords such as intermolecular forces, cohesive forces etc).
4. This reduces the density as it will be light than solid metal due to the high amount of air in the foam. density is the weight of an object compared to its volume/ size. For example if you have a shot-putt that weighs 4kg and a tennis ball, although they are a similar size the tennis ball is no where near as heavy. This is because the shot-putt is more dense.
5. Similar to the answer in Q2. A change in state changes the volume – freezing water increases the volume, this is because molecules have low energy and are not moving freely therefore a solid is formed.
6. For the homogeneous mixture you could just evaporate the water so that you are left with the salt. For the heterogeneous mixture you could use sieving to separate the particles.
Hope this helps out, do just double check what I have written though becuase it has been a while since I done this chemistry lol (I’m assuming you are in secondary school?)
1. elastic property – important to allow plastic bags to withstand heavier products and stretch to fit products.
2. Change in volume, change in state (solid – liquid, liquid – gas), change in temperature (no points for that answer lol). Think of a physical change as something that can be easily reversed. For example, you freeze water it becomes ice, you can then melt the ice to become water (it has changed its state). On the other hand a chemical change is a change in the actual product that can not be reversed. For example, baking a cake, you start of with a whole lot of ingredients then once they are mixed and baked to make a cake you can not reverse the process to get all the ingredients again. (Hope this makes these types of questions a little easier to understand).
3. This is a result of intermolecular forces – attractions between molecules. Water has a strong intermolecular for therefore drops will form on a smooth surface to increase the surface area of the water. (not really the best answer to this question I am sorry but you must have learnt this go back over notes and look for keywords such as intermolecular forces, cohesive forces etc).
4. This reduces the density as it will be light than solid metal due to the high amount of air in the foam. density is the weight of an object compared to its volume/ size. For example if you have a shot-putt that weighs 4kg and a tennis ball, although they are a similar size the tennis ball is no where near as heavy. This is because the shot-putt is more dense.
5. Similar to the answer in Q2. A change in state changes the volume – freezing water increases the volume, this is because molecules have low energy and are not moving freely therefore a solid is formed.
6. For the homogeneous mixture you could just evaporate the water so that you are left with the salt. For the heterogeneous mixture you could use sieving to separate the particles.
Hope this helps out, do just double check what I have written though becuase it has been a while since I done this chemistry lol (I’m assuming you are in secondary school?)
References :